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CrCl Calculator

24-Hour Urine Creatinine Clearance Calculator

A 24-hour urine creatinine clearance measures the patient directly rather than estimating from serum creatinine, which makes it more reliable than Cockcroft-Gault — but only when the collection is complete. This calculator includes the collection-adequacy check that decides whether the result means anything.

Measured creatinine clearance

With collection-adequacy check

mL
hours
Creatinine unit
mg/dL
Sex
yrs
Weight unit
Height unit

Measured creatinine clearance

Example

104.2mL/min

Collection appears complete

Creatinine excretion is 20.0 mg/kg/day, within the expected 20–25 for this sex — consistent with a complete collection.

Normal

Scale: 0–120 mL/min

015306090120+
Per hour
6250 mL/h
BSA-normalised
93.5 mL/min/1.73m²
Compare with the estimate

Measured vs estimated

Measured (this collection)
104.2 mL/min
Estimated (Cockcroft-Gault, ideal weight)
83.3 mL/min
Difference
-20%

Cockcroft-Gault typically overestimates measured clearance by roughly 10–30%. A much larger gap than that usually points at the collection rather than the equation.

Show the working
CrCl = (Ucr × Uvol) / (Scr × minutes)

     = (100 × 1500) / (1 × 1440)
     = 104.17 mL/min

Creatinine excretion: 20.0 mg/kg/day (expected 20–25)

Stays in your browser

  • No patient data stored
  • Free · no signup
  • Pending clinical review

How do you calculate CrCl from a 24-hour urine collection?

CrCl (mL/min) = (urine creatinine × urine volume) / (serum creatinine × collection time in minutes), using 1,440 minutes for a 24-hour collection and the same concentration units for both creatinine values. Unlike Cockcroft-Gault this is a measured clearance rather than an estimate — but it is only as good as the collection, so always check completeness first.

Overview

Measuring clearance instead of estimating it

A timed urine collection measures how much creatinine the kidneys actually excreted over a known period, alongside how much was circulating in the blood. Divide one by the other and you get the volume of plasma cleared per minute — a direct measurement of the patient in front of you, not a population estimate.

That makes it the better option precisely where estimating equations fail: amputees, extremes of muscle mass, unusual body composition, pregnancy, and any situation where a high-consequence dosing decision rests on the number.

The catch is the collection itself. A single missed void invalidates the result, and the resulting figure looks entirely plausible — it is simply wrong, and wrong in the direction of underestimating clearance. That is why the calculator above runs a completeness check automatically rather than leaving it to you to remember.

Methodology

How it is calculated

Measured creatinine clearance
CrCl (mL/min) = (Ucr × Uvol) / (Scr × T)

Ucr  = urine creatinine concentration
Uvol = total urine volume (mL)
Scr  = serum creatinine concentration
T    = collection time in minutes (1,440 for 24 h)

Ucr and Scr must be in the same unit. Mixing mg/dL and µmol/L between the two is a classic error — the calculator above enforces a single unit for both.

BSA normalisation
CrCl (mL/min/1.73 m²) = CrCl × 1.73 / BSA

BSA (Du Bois) = 0.007184 × ht(cm)^0.725 × wt(kg)^0.425

Normalise for comparison with eGFR. Use the un-normalised mL/min figure for drug dosing.

Collecting the sample correctly

  1. 1

    Discard the first morning void

    That urine was produced before the collection window opened. Note the time — this is the start of the collection.

  2. 2

    Collect every void for the next 24 hours

    Every single one, into the supplied container. A missed void is the most common reason the test fails.

  3. 3

    Include the final void at the 24-hour mark

    The last sample is collected at exactly the same clock time as the discarded first void.

  4. 4

    Keep the container refrigerated

    Or on ice, as the laboratory specifies, throughout the collection period.

  5. 5

    Draw a serum creatinine during the window

    Ideally mid-collection. Serum creatinine drawn days apart from the collection undermines the whole calculation.

  6. 6

    Check completeness before acting on the result

    Compare total creatinine excretion against the expected range for the patient’s sex and weight. The calculator does this for you.

The part everyone skips

Was the collection actually complete?

A creatinine clearance from an incomplete collection is worse than an estimate, because it carries the authority of a measurement. Check it every time.
Completeness check
Total creatinine (mg) = Ucr (mg/dL) × Uvol (mL) / 100

Excretion (mg/kg/day) = total × (24 / hours) / weight (kg)

Creatinine excretion is remarkably stable for a given person, which is what makes it a usable check on the collection.

Expected 24-hour creatinine excretion
SexExpected excretionBelow range means
Male20–25 mg/kg/dayProbable missed void
Female15–20 mg/kg/dayProbable missed void
Values decline with age and with reduced muscle mass, so treat the range as a guide rather than a hard rule. A result well below range should prompt a repeat collection rather than a dose change.

What under- and over-collection do to the result

  • Under-collection (a missed void) reduces the measured volume and therefore the calculated clearance. The patient looks like they have worse kidney function than they do, and may be underdosed.
  • Over-collection — usually a collection that ran longer than the stated period — inflates the clearance and risks overdosing.
  • Very high muscle mass or a creatine supplement can also push excretion above range without any collection error.
  • Neither error is visible in the clearance figure itself. Only the excretion check reveals it.

Worked example

58-year-old man, 75 kg. 24-hour collection of 1,500 mL, urine creatinine 100 mg/dL, serum creatinine 1.0 mg/dL.

Urine volume
1,500 mL
Urine creatinine
100 mg/dL
Serum creatinine
1.0 mg/dL
Duration
24 h (1,440 min)
CrCl = (100 × 1500) / (1.0 × 1440)
     = 150,000 / 1,440

Completeness:
  total = 100 × 1500 / 100 = 1,500 mg/day
  1,500 / 75 = 20.0 mg/kg/day  ✓ in range

104.2mL/min

Excretion of 20.0 mg/kg/day sits inside the expected 20–25 range for a man, so the collection is consistent with being complete and the clearance can be trusted.

Comparison

Measured or estimated — which should you use?

Measured versus estimated creatinine clearance
Measured (timed urine)Estimated (Cockcroft-Gault)
What it isA direct measurementA population-derived estimate
Turnaround24 hours plus laboratory timeImmediate
Main failure modeIncomplete collectionAtypical body composition
Best forAmputees, extremes of muscle mass, pregnancy, high-consequence dosingRoutine renal dose checking at the bedside
AccuracyHigh when the collection is completeTypically overestimates measured clearance by 10–30%
PracticalityRequires patient compliance over a full dayRequires four values you already have
Both figures overestimate true GFR, because creatinine is secreted by the renal tubules as well as filtered. For CKD staging use eGFR; for renal drug dosing use the measure the product label specifies.

When a timed collection is worth the effort

  • Amputees, and anyone whose body composition breaks the weight assumption.
  • Very high or very low muscle mass — bodybuilders, cachexia, paraplegia.
  • Pregnancy, where estimating equations are not validated.
  • Before a high-consequence dose: aminoglycosides, chemotherapy, some antivirals.
  • When estimated clearance sits close to a threshold that changes the dose.
  • Vegetarian diets and creatine supplementation, which shift serum creatinine independently of kidney function.

Limitations and sources

  • Only as good as the collection. Completeness is not optional.
  • Assumes stable renal function across the collection window — invalid in acute kidney injury.
  • Still overestimates true GFR because of tubular secretion of creatinine.
  • Requires a serum creatinine drawn during, not days from, the collection.

Levey AS, Inker LA. Assessment of glomerular filtration rate in health and disease. Clin Pharmacol Ther. 2017;102(3):405–19.

KDIGO 2012 Clinical Practice Guideline for CKD. Kidney Int Suppl. 2013;3:1–150.

More calculators

Other calculators on this site

A measured clearance is the escalation path when an estimate is not good enough. For the estimate itself use the Cockcroft-Gault calculator, and for the patients where estimating fails most often, the special populations calculator.

FAQ

Frequently asked questions

Every question this site answers is aggregated on the FAQ hub.

How do you calculate CrCl from a 24-hour urine collection?

CrCl (mL/min) = (urine creatinine × urine volume) / (serum creatinine × collection time in minutes), using 1,440 minutes for a 24-hour collection and the same concentration units for both creatinine values. This is a measured clearance, not an estimate.

How do you know if a urine collection was complete?

Check total creatinine excretion. Men typically excrete 20–25 mg/kg/day and women 15–20 mg/kg/day. A figure below that range usually means a missed void, which will underestimate clearance. The calculator on this page runs that check automatically.

Why does measured CrCl differ from estimated CrCl?

Cockcroft-Gault is a population estimate built from a 1976 cohort of 249 mostly male patients; it typically overestimates measured clearance by 10–30%. A timed collection measures the patient in front of you, but is only as good as the collection — an incomplete one is worse than an estimate.

Security & privacy

Nothing you enter leaves this page

All calculations run entirely in your browser. No patient values are transmitted, logged or stored.

No server round-trip

The equations run as JavaScript on your device. There is no API endpoint that accepts a clinical value, because the calculation code never makes a network request.

Nothing is persisted

Values are not written to a database, a log, local storage or a cookie. Closing the tab discards them.

No account, ever

No signup, no email capture, no paywall. Every calculator works fully without identifying yourself.

One analytics script, and it never sees your values

Google Analytics counts page views. It runs outside the calculator, receives nothing you type, and has ad personalisation switched off. No advertising network, no embedded widgets, no remote fonts.

This is a property of how the site is built, not a policy that could quietly change. Read the full privacy policy or the terms and medical disclaimer.

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Calculate measured creatinine clearance

Enter the collection details and the calculator returns the clearance alongside an automatic completeness check — so you know whether the number can be trusted.

Open the calculatorEstimate with Cockcroft-Gault

Medical disclaimer: This calculator is intended for healthcare professional reference and educational purposes only. It does not replace clinical judgment or the advice of a licensed provider. Always verify dosing decisions against institutional protocol and current prescribing information.