gfr to creatinine clearance calculator

What does this calculator do?

The gfr to creatinine clearance calculator estimates creatinine clearance (CrCl) from an estimated glomerular filtration rate (eGFR). In many lab reports, eGFR is normalized to a standard body surface area (BSA) of 1.73 m². However, medication dosing and some clinical decisions often require an absolute flow rate in mL/min. This tool bridges that gap.

In simple terms: if you know a patient’s eGFR and body size, you can estimate what that filtration number looks like in real, non-normalized mL/min.

Formula used

1) If height and weight are entered

We first estimate body surface area using the Mosteller equation:

BSA (m²) = √((height in cm × weight in kg) / 3600)

2) Convert normalized eGFR to estimated creatinine clearance

Then we convert:

Estimated CrCl (mL/min) = eGFR × (BSA / 1.73)

This is a practical conversion approach when eGFR is already provided by the lab.

Why this conversion matters

• Drug dosing: Some medications are adjusted based on kidney function expressed in mL/min.
• Smaller or larger body size: A normalized eGFR may under- or over-represent absolute filtration.
• Clinical communication: Converting units helps align lab values with prescribing references.

How to use the calculator correctly

1. Enter the eGFR exactly as shown on the lab report (typically mL/min/1.73 m²).
2. Select whether you want to provide BSA directly or calculate it from height and weight.
3. Click Calculate.
4. Review the estimated CrCl and the displayed equation summary.

Example

Suppose eGFR = 60 mL/min/1.73 m², height = 170 cm, weight = 70 kg.

• BSA = √((170 × 70) / 3600) ≈ 1.82 m²
• Estimated CrCl = 60 × (1.82 / 1.73) ≈ 63.1 mL/min

So the estimated absolute creatinine clearance is about 63 mL/min.

Important limitations

• This is an estimation tool, not a measured 24-hour urine creatinine clearance.
• eGFR equations (like CKD-EPI) and Cockcroft-Gault are not interchangeable in every setting.
• Extremes of muscle mass, fluid status, pregnancy, and acute kidney injury can reduce accuracy.
• Always defer to local clinical guidance and licensed medical professionals.

FAQ

Is GFR the same as creatinine clearance?

Not exactly. They are related but derived differently. eGFR is model-based and normalized; measured CrCl is often based on urine collection and serum creatinine.

Can I use this for medication decisions?

Use it for screening and educational understanding. Medication adjustments should be made only by clinicians using validated patient data and prescribing standards.

What if I already know BSA?

Select the direct BSA option and enter it manually. The calculator will skip height/weight and convert right away.