Body Health CalculatorKidney & Filtration
Creatinine Clearance Calculator
Measured creatinine clearance is (urine creatinine × urine volume) / (plasma creatinine × collection time in minutes). A complete 24-hour collection is the usual clinical collection. Clearance overestimates GFR because tubules secrete creatinine.
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Measured clearance from a timed collection
This page does not estimate clearance from age and weight.
It applies the clearance definition to a timed urine collection: CrCl = (UCr × V) / (PCr × t). UCr and PCr must share a concentration unit. V is urine volume in milliliters. t is collection time in minutes. A 24-hour collection uses t = 1440. Shorter complete collections go in the hours field. Incomplete collections, discarded voids, and ice-chest failures are why a “24-hour” result is often fiction.
Measured creatinine clearance still overestimates GFR because of tubular secretion. The gap grows as GFR falls. CKD staging uses estimating equations plus albuminuria. A timed collection is a selected test when muscle mass is unusual or a protocol still asks for measured clearance.
Formula with matching units
Keep plasma and urine creatinine in the same unit before dividing. Both in mg/dL and volume in mL gives mL/min. If urine is µmol/L and plasma is mg/dL, convert one of them. The calculator converts µmol/L to mg/dL by dividing by 88.4.
Example: plasma 1.0 mg/dL, urine 80 mg/dL, volume 1500 mL, 24 hours. CrCl = (80 × 1500) / (1.0 × 1440) = 83 mL/min.
Some labs print 24-hour urine creatinine as grams per day. This page wants concentration and volume, which is how most jugs are resulted. If you only have grams per day, CrCl (mL/min) = (urine creatinine in mg/day) / (plasma creatinine in mg/dL × 14.4). Convert grams to milligrams first. That identity holds when volume is internally consistent.
Worked 24-hour collection
| Input | Value | Role |
|---|---|---|
| Urine creatinine | 80 mg/dL | UCr |
| Urine volume | 1500 mL | V |
| Plasma creatinine | 1.0 mg/dL | PCr |
| Time | 24 h = 1440 min | t |
| CrCl | 83 mL/min | (UCr × V) / (PCr × t) |
How to use the creatinine clearance calculator
Copy numbers from one collection episode. Do not pair last month’s plasma creatinine with this week’s jug.
Enter the hours you actually collected, not 24 if the jug closed early. Match units to the report. Urine creatinine is often a high number in mg/dL. Plasma creatinine is usually near 1. Swap them and the result is huge or near zero. Recheck before acting.
Read the clearance against a completeness check and against eGFR. A 20% gap versus 2021 eGFR can be secretion, an incomplete collection, or both.
How to collect the urine
Start after emptying the bladder and discarding that void. Write the start time.
Collect every later void, including overnight, into the laboratory jug. At the stop time, void again and add that sample. One missed void underestimates volume and clearance. Keep the jug as the laboratory instructs, often refrigerated. Do not add water to “help” volume. Hydration should be usual unless a protocol says otherwise. Hard exercise during the collection can change creatinine excretion.
Draw plasma creatinine during the collection window, usually the morning the jug comes back. A creatinine drawn days later after a meat-heavy meal is the wrong denominator.
Checking whether the collection was complete
Expected 24-hour creatinine excretion is often about 15 to 20 mg/kg actual body weight in younger men, lower in older adults and in many women, with wide scatter.
A 70 kg man who excretes 400 mg/day almost certainly missed voids or diluted the report. A 120 kg man who excretes 2800 mg/day may have over-collected or hit a unit error. Excretion is UCr (mg/dL) × V (dL). 1500 mL is 15 dL, so 80 mg/dL × 15 dL = 1200 mg/day. For a 70 kg man that is 17 mg/kg, a plausible complete collection. The same 80 mg/dL in 600 mL is 480 mg/day (6.9 mg/kg) and should not dose a drug.
Volume alone is a weak check. 400 mL can be a complete oliguric collection. 4 L can be complete in polydipsia. Combine volume, excretion, and missed-void history. If completeness is doubtful, repeat the collection or use eGFR plus ACR. Do not force a dosing decision from a bad jug.
Problems that bias measured creatinine clearance
| Problem | Effect on CrCl | What to do |
|---|---|---|
| Missed void | Underestimate | Repeat collection |
| Over-collection past 24 h | Overestimate | Use actual hours in the formula |
| Tubular secretion | Overestimate vs GFR | Expect this, especially at low GFR |
| Cimetidine or trimethoprim | Lower measured and estimated values | Review medicines |
How this differs from eGFR
eGFR equations use a blood sample and are indexed to 1.73 m². Measured clearance uses urine plus blood and is unindexed mL/min. Comparing them needs body surface area.
When muscle mass is typical, 2021 CKD-EPI is the practical staging tool. When muscle is atypical and cystatin C is missing, a careful collection can still help. It is not automatically more accurate than a good equation. Children, pregnancy, and unstable AKI need methods chosen by the treating team. A 24-hour collection during rapidly changing GFR averages a moving target.
To compare with indexed eGFR, convert: indexed CrCl = CrCl × 1.73 / BSA. For BSA 1.90 m² and CrCl 83 mL/min, indexed clearance is 83 × 1.73 / 1.90 = 76 mL/min/1.73 m². Only then does a 2021 eGFR of 70 sit in the same units. Research protocols sometimes use cimetidine to block creatinine secretion and pull clearance closer to GFR. That is not a home maneuver. Do not take cimetidine to “improve” a calculator result.
Twelve-hour collections
If the laboratory validates a 12-hour collection, enter 12 in the hours field.
For UCr 90 mg/dL, V 800 mL, PCr 1.1 mg/dL, t = 720 minutes: CrCl = (90 × 800) / (1.1 × 720) = 91 mL/min. Doubling a 12-hour volume to fake a 24-hour collection is wrong when overnight and daytime excretion differ. Overnight-only collections miss daytime creatinine after meals. Daytime-only collections miss the lower overnight rate. 24 hours remains the default when the test is worth doing.
Using the number in care
Bring the laboratory printout, not only this calculator result, to the clinician who ordered the collection.
Dosing staff need the raw UCr, V, PCr, and hours. If clearance will adjust a nephrotoxic drug, confirm the collection was complete the same day. Do not recycle last year’s jug math.
Pair any clearance with ACR if the question is CKD. Clearance does not measure albumin leak.
Limitations
The formula assumes complete recovery of urine creatinine and a stable plasma level. Extra-renal loss, degradation in the jug, and post-renal obstruction break that story.
This page will compute a 6-hour collection if you enter 6 hours. That does not make six hours equal to 24 physiologically. Follow the laboratory’s validated length. Seek urgent care for anuria, refractory hyperkalemia, or uremic symptoms. A clearance calculator has no role there.
Creatinine in the jug can degrade if the sample sits warm. Bacteria can consume it. Surprisingly low excretion with a story of a complete collection should prompt a refrigerated repeat, not a hyperfiltration diagnosis. People with diverted urine (ileal conduit, nephrostomy) need a protocol that captures all output. A toilet collection misses diverted urine and understates clearance.
How it works
CrCl (mL/min) = (UCr × V) / (PCr × t). Concentrations must be in the same mass/volume unit. V is milliliters. t is minutes (hours × 60).
Frequently asked questions
- Why collect urine for 24 hours?Creatinine excretion varies during the day. A full day reduces timing error compared with a short collection, but missed voids still ruin the result.
- Is measured clearance better than eGFR?It is a different test. It can help when muscle mass is unusual, but incomplete collection, extra-renal creatinine, and tubular secretion all bias it. Measured GFR with an exogenous marker remains the reference.
- What if my collection was 12 hours?Enter the actual hours. Do not scale a partial collection as if it were 24 hours unless a laboratory protocol does that conversion from a complete short collection.