                  FOR PUBLICATION
  UNITED STATES COURT OF APPEALS
       FOR THE NINTH CIRCUIT

TUTOR-SALIBA CORPORATION, a            
California Corporation; RONALD N.
TUTOR, an Individual,
              Plaintiffs-Appellants,
                v.                          No. 04-35424
CITY OF HAILEY, a Municipal                  D.C. No.
                                           CV 02-0475 BLW
Corporation; BOARD OF
TRUSTEES OF THE FRIEDMAN                      OPINION
MEMORIAL AIRPORT AUTHORITY;
FRIEDMAN MEMORIAL AIRPORT
AUTHORITY,
             Defendants-Appellees.
                                       
        Appeal from the United States District Court
                  for the District of Idaho
         B. Lynn Winmill, District Judge, Presiding

                 Argued and Submitted
            March 10, 2006—Portland, Oregon

                     Filed July 3, 2006

     Before: Melvin Brunetti, A. Wallace Tashima, and
             Richard A. Paez, Circuit Judges.

                 Opinion by Judge Tashima




                            7309
               TUTOR-SALIBA CORP. v. CITY OF HAILEY                  7313


                              COUNSEL

Patrick E. Bailey, Bailey & Partners, Santa Monica, Califor-
nia, for the plaintiffs-appellants.

W. Eric Pilsk, Akin Gump Strauss Hauer & Feld, LLP, Wash-
ington, D.C., for the defendants-appellees.


                              OPINION

TASHIMA, Circuit Judge:

   Plaintiff Ronald N. Tutor (“Tutor”) filed this action after
defendants denied him permission to land his Boeing Busi-
ness Jet at Friedman Memorial Airport in Hailey, Idaho. Tutor
brought several claims under 42 U.S.C. § 1983. The district
court granted defendants summary judgment on all claims,
and defendants subsequently filed a post-judgment motion for
attorney’s fees and costs under 42 U.S.C. § 1988.1 The district




  1
   We note that the costs at issue here were awarded under § 1988 and not
under Fed. R. Civ. P. 54(b). The court thus was not restricted to statutory
items of costs under 28 U.S.C. § 1920, but had the discretion to award out
of pocket expenses and costs. See Davis v. Mason County, 927 F.2d 1473,
1487-88 (9th Cir. 1991) (holding that reasonable out of pocket expenses
that are normally billed to fee-paying clients may be awarded as costs
under § 1988).
7314           TUTOR-SALIBA CORP. v. CITY OF HAILEY
court found that all but two of the bases of Tutor’s § 1983
claim were frivolous; it therefore granted defendants’ motion
in part for fees and costs incurred in defending against Tutor’s
frivolous claims, while denying the motion with respect to
fees and costs incurred in defending against Tutor’s non-
frivolous claims.

   Tutor then moved to vacate the fee order, arguing that: (1)
the district court applied an improper legal standard when
evaluating the § 1988 motion for attorney’s fees and costs; (2)
because the district court found that two bases of the § 1983
claim were not frivolous, the entire § 1983 cause of action
was necessarily not frivolous; and (3) the district court’s fee
allocation, including costs, was unreasonable and not sup-
ported by the record. The district court denied Tutor’s motion
to vacate and Tutor now raises the same arguments on appeal.
We have jurisdiction under 28 U.S.C. § 1291 over this post-
judgment order. We affirm the district court’s conclusion that
defendants were entitled to partial attorney’s fees and costs
incurred in defending against Tutor’s frivolous claims. How-
ever, because the district court failed to explain adequately
how it arrived at the amount of its attorney’s fee and cost
award, we vacate the award and remand so that the district
court may further elucidate its reasoning.

            FACTUAL AND PROCEDURAL BACKGROUND

   Defendants operate Friedman Memorial Airport, which is
a single-runway airport serving the resort areas of Hailey,
Ketchum, and Sun Valley, Idaho. Tutor owns a vacation home
in Ketchum and requested permission to land his personal
Boeing Business Jet2 at the airport in order to access his vaca-
tion home.
  2
   The aircraft is owned by plaintiff Tutor-Saliba Corporation and is the
business, or executive, version of the Boeing 737.
             TUTOR-SALIBA CORP. v. CITY OF HAILEY         7315
   The airport maintains a runway weight restriction that pro-
hibits operations by dual-wheel aircraft with a maximum
gross take-off weight of 95,000 pounds or more. Tutor’s Boe-
ing Jet has a maximum gross take-off weight of 171,000
pounds. Defendants applied this weight restriction and denied
Tutor’s request to operate his Boeing jet at the airport.
Although Tutor was denied permission to operate his Boeing
jet at the airport, he was able to access his vacation home by
using an alternative private jet that met the airport’s weight
requirements.

   Tutor’s complaint challenged defendants’ restriction as vio-
lating substantive due process, procedural due process, equal
protection, and right to travel and his rights under the Com-
merce Clause, the Airport and Airway Improvement Act of
1982, 49 U.S.C. §§ 47101-47131 (2004) (“AAIA”), the Air-
port Noise and Capacity Act of 1990, 49 U.S.C. §§ 47521-
47533 (2004) (“ANCA”), and state law. Tutor sought dam-
ages pursuant to 42 U.S.C. § 1983, as well as declaratory and
injunctive relief, and attorney’s fees under 42 U.S.C. § 1988.

   Following discovery, both sides moved for summary judg-
ment. The district court denied Tutor’s motion for summary
judgment and granted defendants’ motion for summary judg-
ment on all claims, finding that a number of Tutor’s claims
were frivolous. Defendants subsequently moved for attorney’s
fees and costs pursuant to Federal Rule of Civil Procedure 54
and 42 U.S.C. § 1988. The district court granted defendants’
motion in part, concluding that all of Tutor’s constitutional
claims, i.e., his substantive due process, procedural due pro-
cess, equal protection, Commerce Clause, and right to travel
claims, were frivolous. It also found, however, that Tutor’s
AAIA and ANCA claims were issues of first impression, and
therefore were not frivolous. After reviewing the record,
briefs, and legal bills, the district court determined that 20
percent of defendants’ legal fees were attributable to defend-
ing against the frivolous constitutional claims. It then found
that the hourly rate charged by defendants’ counsel was rea-
7316             TUTOR-SALIBA CORP. v. CITY OF HAILEY
sonable for the skill and experience of the lawyers and
awarded $88,094.05 in legal fees, representing 20 percent of
the total fees requested, plus $70,944.39 in costs, mostly for
travel and depositions. The district court denied defendants’
request for expert fees and costs. It also denied Tutor’s
motion to vacate the fee award. Tutor appeals the fee award.3

                        STANDARD OF REVIEW

   A district court’s decision to award attorney’s fees is
reviewed for abuse of discretion. Richard S. v. Dep’t of
Developmental Servs., 317 F.3d 1080, 1085 (9th Cir. 2003).
“Elements of legal analysis and statutory interpretation that
figure into the district court’s attorney’s fees decision are
reviewed de novo.” Id. at 1086 (citation omitted). Factual
findings supporting the decision are reviewed for clear error.
Id.

                               DISCUSSION

I.       Tutor’s constitutional claims were frivolous.

   [1] In addition to relief available under 42 U.S.C. § 1983,
§ 1988 provides, in relevant part, that “the court, in its discre-
tion, may allow the prevailing party . . . a reasonable attor-
ney’s fee as part of the costs.” 42 U.S.C. § 1988(b). The
Supreme Court has instructed that a prevailing defendant in a
§ 1983 action is entitled to an attorney’s fees award under
§ 1988 only when the plaintiff’s action is “frivolous, unrea-
sonable, or without foundation.” Hughes v. Rowe, 449 U.S. 5,
14 (1980) (per curiam) (quoting Christiansburg Garment Co.
v. EEOC, 434 U.S. 412, 421 (1978)). In determining whether
this standard has been met, a district court must assess the
claim at the time the complaint was filed, and must avoid
     3
    Tutor also separately appealed the district court’s decision on the mer-
its. That appeal was dismissed for failure to file an opening brief. Tutor
v. City of Hailey, No. 04-35156 (9th Cir. Jul. 20, 2004) (order).
             TUTOR-SALIBA CORP. v. CITY OF HAILEY           7317
“post hoc reasoning by concluding that, because a plaintiff did
not ultimately prevail, his action must have been unreasonable
or without foundation.” Warren v. City of Carlsbad, 58 F.3d
439, 444 (9th Cir. 1995) (internal quotation marks and cita-
tions omitted); Christiansburg, 434 U.S. at 421-22.

  A.   The district court applied the proper legal standard.

   Tutor first argues that the district court erred by applying
an incorrect legal standard when it evaluated whether his con-
stitutional claims were frivolous, unreasonable, or without
foundation. Tutor contends that the district court improperly
relied on evidence offered by the parties in support of their
motions for summary judgment and its review of the record
and its own assessment of Tutor’s claims, rather than on the
nature of the claims at the outset of the litigation.

   [2] The only support Tutor offers for his argument is a
string of partial quotes from the district court’s opinions.
Tutor contends that the quotes prove that the district court
applied “post-hoc reasoning” and “hindsight logic” because
they are in the past tense. A review of the district court’s rul-
ings, however, belies Tutor’s argument. In its summary judg-
ment ruling, the district court cited to Christiansburg,
indicating that it was aware of the proper legal standard. The
district court also carefully evaluated each of Tutor’s claims
and focused on whether there was any colorable legal or fac-
tual basis for each claim.

   [3] Moreover, in response to Tutor’s motion to vacate, the
district court expressly stated that its decision was based on
the fact that Tutor “could not, even at the outset of the litiga-
tion, establish that [he] had a Constitutionally protected right
to operate [his] preferred aircraft at [his] preferred airport.”
See Head v. Medford, 62 F.3d 351, 356 (11th Cir. 1995) (per
curiam) (reversing the denial of attorney’s fees after summary
judgment because “the assertion of a constitutional claim
based knowingly on a nonexistent property interest was
7318          TUTOR-SALIBA CORP. v. CITY OF HAILEY
legally groundless”); Flowers v. Jefferson Hosp. Ass’n, 49
F.3d 391, 392-93 (8th Cir. 1995) (per curiam) (affirming fee
award where district court “specifically considered the
Supreme Court’s admonition in Christiansburg to refrain
from post hoc reasoning and to view the reasonableness of the
matter from the plaintiff’s perspective at the time”). Accord-
ingly, we conclude that the district court applied the proper
legal standard when it determined that Tutor’s constitutional
claims were frivolous.

  B.     Tutor’s constitutional claims were frivolous.

    We next examine whether the district court abused its dis-
cretion when it concluded that Tutor’s constitutional claims
were frivolous at the outset of the litigation. See Christians-
burg, 434 U.S. at 421; Thomas v. City of Tacoma, 410 F.3d
644, 650 (9th Cir. 2005). Tutor argues that his constitutional
claims were not frivolous because they were supported by
existing case law. Although Tutor cites various cases which
he contends demonstrate that his claims were not frivolous, as
we explain below, we conclude that the district court did not
abuse its discretion when it found that Tutor lacked a factual
and legal basis for his constitutional claims at the outset of the
litigation.

    1.    Substantive Due Process

   Tutor alleged that the airport’s runway weight limitation
violated his substantive due process right because it denied
him access to the airport and his real property in Ketchum,
Idaho. To establish a violation of substantive due process, a
plaintiff must first show a deprivation of some fundamental
right or liberty interest that is “deeply rooted in this Nation’s
history and tradition.” Washington v. Glucksberg, 521 U.S.
702, 720-21 (1997) (internal quotation marks omitted). We
need not address whether Tutor was deprived of a fundamen-
tal right, however, because Tutor’s complaint makes it clear
             TUTOR-SALIBA CORP. v. CITY OF HAILEY          7319
that he was not deprived of access to the airport or to his
vacation home.

   [4] Tutor knew or should have known that his substantive
due process claim lacked merit at the outset of the litigation
because he had continuous access to the airport, and his vaca-
tion home, through the use of an alternative aircraft. Accord-
ingly, the district court did not abuse its discretion when it
found that this claim was frivolous.

    2.   Procedural Due Process

   To establish a violation of procedural due process a plain-
tiff must demonstrate: (1) a deprivation of a constitutionally
protected liberty or property interest, and (2) a denial of ade-
quate procedural protections. Brewster v. Bd. of Educ. of Lyn-
wood Unified Sch. Dist., 149 F.3d 971, 982 (9th Cir. 1998).

  [5] As noted above, Tutor was not deprived of a liberty or
property interest because he was able to access his vacation
home by use of another aircraft. Accordingly, the district
court did not abuse its discretion when it found that Tutor
knew that this claim was frivolous from the outset of the liti-
gation.

    3.   Equal Protection

   Tutor claimed that the runway weight limitation violates
the Equal Protection Clause on the grounds that: (1) aircraft
similar to the Boeing Business Jet were permitted to operate
at the airport; (2) in the past the airport permitted aircraft
weighing more than 95,000 pounds to operate; and (3) basing
the rule on maximum certified take-off weight, rather than
actual operating weight, was arbitrary.

  In order to determine whether a regulatory classification
violates the Equal Protection Clause, courts consider first
whether the classification is based on a suspect class or impli-
7320          TUTOR-SALIBA CORP. v. CITY OF HAILEY
cates fundamental rights. Nordlinger v. Hahn, 505 U.S. 1, 10
(1992). If so, the classification is evaluated under a height-
ened standard. Id. If not, the classification is evaluated under
the “rational basis” standard. Id.

   It is clear that aircraft weight is not a suspect classification,
and there is no fundamental right to land an aircraft at any
particular airport. See Hager v. City of West Peoria, 84 F.3d
865, 872 (7th Cir. 1996) (“Access to real property does not
rise to the level of a fundamental right such that its denial
merits heightened scrutiny.”). Therefore, rational basis review
applies.

   Under rational basis review, the Equal Protection Clause is
satisfied if: (1) “there is a plausible policy reason for the clas-
sification,” (2) “the legislative facts on which the classifica-
tion is apparently based rationally may have been considered
to be true by the governmental decisionmaker,” and (3) “the
relationship of the classification to its goal is not so attenuated
as to render the distinction arbitrary or irrational.” Nordlinger,
505 U.S. at 11 (citations omitted).

   [6] Tutor’s arguments do not overcome the obvious rational
basis for the weight limitation. Since the weight restriction is
closely related to the defendants’ interest in preserving the
condition of the runway, and Tutor had no factual basis to
support his contention that the defendants permitted other air-
craft exceeding the 95,000 pound maximum take-off weight
to operate at the airport, the district court did not abuse its dis-
cretion when it concluded that Tutor knew or should have
known that this claim was frivolous.

    4.   Impermissible Burden on Interstate Commerce

   [7] Tutor argued that defendants’ ban on dual-wheel air-
craft with a maximum take-off weight in excess of 95,000
pounds is an impermissible burden on interstate commerce.
To prove a Commerce Clause violation, Tutor had the burden
              TUTOR-SALIBA CORP. v. CITY OF HAILEY        7321
of showing that defendants’ restriction has the effect of dis-
criminating against out-of-state interests as compared to in-
state interests, or was imposed with the primary purpose of
regulating interstate commerce. Hughes v. Oklahoma, 441
U.S. 322, 336 (1979). Tutor, however, merely asserted that he
believed the ban was an impermissible burden on interstate
commerce without offering any evidence to support the claim.
Tutor offered no evidence indicating that the ban had any-
thing more than an incidental effect on interstate commerce or
that the weight restriction was imposed for an impermissible
purpose, rather than the obvious purpose of promoting the
safety of the airport by preventing deterioration of its run-
ways. Accordingly, the district court did not abuse its discre-
tion when it found that Tutor knew or should have known that
this claim was frivolous from the outset of the litigation.

      5.   Right to Travel

   [8] Tutor claimed that defendants’ ban on dual-wheel air-
craft with a maximum take-off weight in excess of 95,000
pounds denied him his right to travel as guaranteed by the
Fourteenth Amendment to the United States Constitution. We
have previously held, however, that “burdens on a single
mode of transportation do not implicate the right to interstate
travel.” Miller v. Reed, 176 F.3d 1202, 1205 (9th Cir. 1999)
(citations omitted). Here, Tutor’s right to travel was not vio-
lated because he was able to use a different private jet to
access his vacation home. In addition, Tutor could have flown
into a different airport, flown on a commercial airliner, or
used another mode of transportation. Accordingly, the district
court did not abuse its discretion when it concluded that Tutor
knew or should have known, from the outset of the litigation,
that this claim was frivolous.

II.   A § 1988 fee award is proper when distinct frivolous
      claims are joined with non-frivolous claims.

   Having concluded that the district court did not abuse its
discretion when it found that Tutor’s constitutional claims
7322         TUTOR-SALIBA CORP. v. CITY OF HAILEY
were frivolous, we must next decide whether attorney’s fees
may be awarded to a defendant in a § 1983 action when frivo-
lous claims are joined with claims that are not frivolous.

   [9] Tutor argues that the district court’s determination that
two of the bases of his § 1983 claim were not frivolous pre-
cludes an award of attorney’s fees under § 1988. While this
is an issue of first impression in this circuit, we find the
Supreme Court’s decision in Hensley v. Eckerhart, 461 U.S.
424 (1983), instructive. In Hensley, the Court decided
whether plaintiffs could recover partial attorney’s fees when
they brought both successful and unsuccessful claims. Id. at
440. The Court held that plaintiffs could recover partial fees
in situations where their unsuccessful claims were “distinct in
all respects from [their] successful claims.” Id. Although the
Court acknowledged that there is “no certain method of deter-
mining when claims are related or unrelated,” id. at 437 n.12
(internal quotation marks omitted), it explained that claims
involving a common core of facts, or based on related legal
theories, should not be viewed as a series of discrete claims
because “[m]uch of counsel’s time will be devoted generally
to the litigation as a whole, making it difficult to divide the
hours expended on a claim-by-claim basis,” id. at 435. The
Court also noted, in dicta, that a defendant could recover
attorney’s fees in situations where a plaintiff succeeds on one
claim, but also asserts a frivolous claim unrelated to the suc-
cessful claim. Id. at 435 n.10.

    Some circuits have concluded that, where a plaintiff’s friv-
olous and non-frivolous claims are sufficiently intertwined,
the defendant cannot recover attorney’s fees for the time spent
defending against the frivolous claims. See Colombrito v.
Kelly, 764 F.2d 122, 132 (2d Cir. 1985) (reversing district
court’s award of attorney’s fees where plaintiff’s frivolous
and non-frivolous claims were closely intertwined, and con-
tinuation of the meritless claim past discovery had only mini-
mal effect on the time and other resource costs of the
litigation); Tarter v. Raybuck, 742 F.2d 977, 987-88 (6th Cir.
             TUTOR-SALIBA CORP. v. CITY OF HAILEY            7323
1984) (finding that the district court abused its discretion in
awarding attorney’s fees to the defendant because action that
included one non-frivolous claim was not wholly meritless or
without foundation).

   Tutor similarly argues that the district court erred in award-
ing defendants partial fees because his § 1983 claim is a sin-
gle, interrelated claim that arises from a common set of facts.
This argument finds support in Hensley, which instructs that
claims involving a common core of facts, or related legal the-
ories, should not be viewed as a series of discrete claims for
purposes of awarding a prevailing plaintiff attorney’s fees.
See 461 U.S. at 435. In addition, the legislative history behind
§ 1988 demonstrates Congress’ intent to promote vigorous
private enforcement of civil rights, see S. Rep. 94-1101
(1976), and permitting district courts to parse out frivolous
claims from a set of interrelated claims may chill such
enforcement. See Miller v. Los Angeles County Bd. of Educ.,
827 F.2d 617, 619 (9th Cir. 1987) (“The strict nature of the
Christiansburg standard is premised on the need to avoid
undercutting Congress’ policy of promoting vigorous prose-
cution of civil rights violations under Title VII and § 1983.”).

   [10] Other circuits, however, have permitted an award of
attorney’s fees for defending against frivolous claims even
where frivolous and non-frivolous claims are interrelated. See,
e.g., Ward v. Hickey, 996 F.2d 448 (1st Cir. 1993). In Ward,
the First Circuit held that interrelation between claims was
only one factor in the award of attorney’s fees, and could not
be used “to decide not to grant any fees.” Id. at 455. The court
concluded that, despite the high bar defendants must satisfy
to receive fees in civil rights cases, fee awards are still neces-
sary to deter frivolous claims and that “a district court should
not deny fees for defending frivolous claims merely because
calculation would be difficult.” Id. at 455-56.

   [11] In Quintana v. Jenne, 414 F.3d 1306 (11th Cir. 2005),
the Eleventh Circuit approved Ward’s reasoning and affirmed
7324           TUTOR-SALIBA CORP. v. CITY OF HAILEY
a district court’s award of attorney’s fees for defending
against a claim it found frivolous, while reversing the district
court’s award of fees for the defense against a claim that was
not frivolous. Id. at 1312. The court explained that it would
“undermine the intent of Congress to allow plaintiffs to prose-
cute frivolous claims without consequences merely because
those claims were joined with unsuccessful claims that were
not frivolous.” Id. Although the court recognized that the
plaintiff’s claims arose from a common set of facts, it rea-
soned that the plaintiff’s claims were not intertwined because
the plaintiff had distinguished the claims in his complaint and
had advanced sufficiently distinct arguments. Id. Accordingly,
the court remanded the case to the district court so that it
could “weigh and assess the amount of attorney’s fees attrib-
utable exclusively to [plaintiff’s frivolous claim].” Id.

   [12] We find the Eleventh Circuit’s reasoning in Quintana
persuasive. Here, Tutor’s constitutional and statutory claims
were distinct and the merits of each claim could easily be
evaluated separately. Throughout the district court proceed-
ings, from the complaint through the summary judgment
briefing, the constitutional and statutory claims were argued
separately. The fact that Tutor’s claims arose from the same
basic set of facts does not alter our assessment of the distinc-
tive nature of his claims. Notably, the factual record was not
complex and the parties did not dispute the material facts
underlying Tutor’s claims. The dispute centered on the legal
conclusions that could be drawn from — the legal signifi-
cance of — the undisputed facts. We reject Tutor’s proposed
rule, under which entitlement to attorney’s fees would depend
not upon the district court’s review of the merits of a plain-
tiff’s § 1983 claims, but upon how a plaintiff chose to draft
his complaint. Instead, we conclude that because Tutor’s con-
stitutional claims were sufficiently distinct from his statutory
claims, the district court was in a position properly to weigh
and assess the amount of fees attributable to Tutor’s frivolous
claims. See Quintana, 414 F.3d at 1312.4 We thus hold that
  4
   Because we conclude that Tutor’s claims were not intertwined, we do
not reach the question of whether a district court may award partial attor-
               TUTOR-SALIBA CORP. v. CITY OF HAILEY                 7325
the district court did not err in awarding defendants fees for
defending against Tutor’s frivolous constitutional claims.

III.   Determination of the amount of the award must be
       adequately explained.

   Finally, Tutor argues that the district court abused its dis-
cretion in determining the amount of the fee award because
the award is unreasonable and not supported by the record.
In setting the amount of an attorney’s fees award under
§ 1988, a district court must utilize the “lodestar” method of
calculating the award, which is accomplished by multiplying
the number of hours reasonably expended on the litigation by
a reasonable hourly rate. Hensley, 461 U.S. at 433. The
Supreme Court has established “a strong presumption that the
lodestar represents the reasonable fee.” City of Burlington v.
Dague, 505 U.S. 557, 562 (1992) (citation and internal quota-
tion marks omitted). This court also requires consideration of
the 12-factor Kerr test. See Kerr v. Screen Extras Guild, Inc.,
526 F.2d 67, 70 (9th Cir. 1975).

    [13] Although “[t]he determination of attorney fees is
within the sound discretion of the trial court and will not be
disturbed absent an abuse of discretion,” Zuniga v. United
Can Co., 812 F.2d 443, 454 (9th Cir. 1987) (citation omitted),
the Supreme Court has directed that “[i]t remains important
. . . for the district court to provide a concise but clear expla-
nation of its reasons for the fee award.” Hensley, 461 U.S. at
437. If the district court fails to provide a clear indication of
how it exercised its discretion, we will remand the award for
the court to provide an explanation. See D’Emanuele v. Mont-
gomery Ward & Co., Inc., 904 F.2d 1379, 1384-86 (9th Cir.
1990), overruled on other grounds by Dague, 505 U.S. 557.

ney’s fees where frivolous claims are combined with non-frivolous claims
and the claims are not sufficiently distinct. See, e.g., Ward, 996 F.2d at
455.
7326         TUTOR-SALIBA CORP. v. CITY OF HAILEY
   For example, in Chalmers v. City of Los Angeles, 796 F.2d
1205 (9th Cir. 1986), we vacated and remanded an attorney’s
fee award for failure to provide a clear but concise explana-
tion. Id. at 1213. We explained that “the district court failed
to indicate what number of hours were being compensated
and what hourly rate was applied.” Id. There, the district court
also reduced the fee award to reflect the plaintiff’s lack of
complete success, but failed to “articulate with sufficient clar-
ity the manner in which it [made] its determination of a rea-
sonable hourly rate and the number of hours which should be
reasonably compensated.” Id. at 1211; see also McGrath v.
County of Nevada, 67 F.3d 248, 254 (9th Cir. 1995) (vacating
and remanding an attorney’s fee award because the district
court insufficiently explained how it arrived at the award);
D’Emanuele, 904 F.2d at 1384-86 (same).

   [14] Here, defendants’ counsel submitted detailed time
records, an affidavit setting forth his experience and back-
ground, and his billing rates and practices. The affidavit, how-
ever, failed adequately to separate out what percentage of fees
were incurred on each claim. Although the district court stated
that it utilized the “lodestar” method to calculate the fee
award, and that it had considered the factors enunciated in
Kerr, 526 F.2d at 70, its order failed to reveal the number of
hours being compensated, the hourly rate being applied, and
how it reached the conclusion that 20 percent of counsel’s
time and costs were apportionable to the defense against
Tutor’s frivolous claims. As we explained in Chalmers:

    We recognize that deference is to be given to a dis-
    trict court’s determination of a reasonable attorney’s
    fee. Nonetheless, it remains important for the district
    court to provide an adequate explanation of the rea-
    sons for its award and the manner in which that
    award was determined. Here, while the order does
    indicate that the Kerr factors were considered, the
    district court failed to indicate what number of hours
    were being compensated and what hourly rate was
             TUTOR-SALIBA CORP. v. CITY OF HAILEY             7327
    applied. . . . Without some indication or explanation
    of how the district court arrived at the amount of fees
    awarded, it is simply not possible for this court to
    review such an award in a meaningful manner.
    Absent some indication of how the district court’s
    discretion was exercised, this court has no way of
    knowing whether that discretion was abused.

796 F.2d at 1213.

   [15] Because the district court failed to provide a suffi-
ciently detailed explanation of how it reached its award, the
award of fees and costs must be vacated and remanded so that
the district court can provide that explanation.

                          CONCLUSION

   The district court did not abuse its discretion in concluding
that Tutor’s constitutional claims were frivolous, because
Tutor knew or should have known that he had no factual basis
for his constitutional claims at the outset of the litigation. The
district court also properly concluded that defendants were
entitled to a partial award of attorney’s fees and costs incurred
in defending against Tutor’s frivolous claims. However,
because the district court failed adequately to explain how it
arrived at the amount of its award, we vacate the attorney’s
fee and costs order and remand so that the district court may
further elucidate its reasoning. Each party shall bear its own
costs on appeal.

 AFFIRMED           in   part,    award      VACATED          and
REMANDED.
