Aaron Graves, PhDude (Replica)

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gfr clearance calculator

Posted on February 16, 2026 by Admin

Creatinine Clearance (Measured GFR Proxy)

Use this calculator with a timed urine collection to estimate kidney filtration performance.

Common timed collections are 24 hours.
This tool is educational and not a diagnosis. Lab methods, muscle mass, medications, hydration, and collection errors can influence results. Discuss abnormal numbers with a qualified clinician.

What this GFR clearance calculator measures

This page calculates creatinine clearance, a practical estimate of kidney filtration based on blood and urine data. While it is not identical to a formally measured GFR with specialized tracer testing, it is widely used in routine care.

If your provider asked for a timed urine collection, this is typically the equation they are using to convert lab values into a clearance result expressed in mL/min.

Formula used

Primary equation

Creatinine clearance (CrCl) = (UCr × V̇) / SCr

  • UCr = urine creatinine concentration (mg/dL)
  • SCr = serum creatinine concentration (mg/dL)
  • V̇ = urine flow rate in mL/min (total urine volume ÷ collection minutes)

Optional body-size correction

When height and weight are entered, the calculator estimates body surface area (BSA) using the Mosteller equation:

BSA = √[(height in cm × weight in kg) / 3600]

Then it reports a normalized clearance:
CrCl (normalized to 1.73 m²) = CrCl × (1.73 / BSA)

How to get accurate inputs

  • Follow lab instructions exactly for start time and end time of urine collection.
  • Include all urine during the collection window.
  • Confirm units are mg/dL for both urine and serum creatinine.
  • Use the correct total volume in mL from the lab or collection container measurement.
  • If anything was missed during collection, tell your care team.

How to interpret results

The calculator provides a rough kidney function category using common GFR cut points:

  • G1: 90+ mL/min/1.73 m²
  • G2: 60–89
  • G3a: 45–59
  • G3b: 30–44
  • G4: 15–29
  • G5: <15

A single value should not be interpreted alone. Trends over time, urine protein/albumin, blood pressure, diabetes status, and clinical context are all essential.

Important limitations

Collection quality matters

The most common source of error is an incomplete urine collection. Missing urine can make clearance appear lower than true function.

Creatinine is not perfect

Creatinine production varies by muscle mass, diet, and age. Some medications also alter serum creatinine handling.

Not a substitute for medical care

Use this calculator as a support tool. Diagnosis and treatment decisions should come from a licensed clinician.

Quick example

Suppose:

  • UCr = 100 mg/dL
  • SCr = 1.0 mg/dL
  • Urine volume = 1440 mL
  • Collection time = 24 hours (1440 minutes)

Flow rate V̇ = 1440 ÷ 1440 = 1 mL/min.
CrCl = (100 × 1) ÷ 1.0 = 100 mL/min.

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