What the creatinine clearance (IBW) calculator does
This calculator estimates creatinine clearance (CrCl) with the Cockcroft-Gault equation, but with one key difference from a plain-weight version: it uses your ideal body weight (IBW) instead of your actual weight. It first derives IBW from your height and sex with the Devine formula, then feeds that value into Cockcroft-Gault. Using IBW is a common clinical convention because actual weight can overestimate clearance in people carrying extra body fat, which contributes little to creatinine production.
How to use it
Select your sex, then enter your age in years, your height in centimetres, and your serum creatinine in mg/dL (from a blood test). The tool converts your height to inches, calculates ideal body weight, and returns your estimated creatinine clearance in mL/min along with a kidney-function category. Leave a field blank and the calculator simply waits for your input rather than guessing from defaults.
The formula explained
Ideal body weight uses the Devine (1974) formula, where h is height in inches (h equals height in cm divided by 2.54):
$$ \text{IBW (male)} = 50 + 2.3 \times (h - 60) $$ $$ \text{IBW (female)} = 45.5 + 2.3 \times (h - 60) $$That ideal weight is then used in the Cockcroft-Gault equation, where Scr is serum creatinine in mg/dL and S is a sex factor (1 for men, 0.85 for women):
$$ \text{CrCl} = \frac{(140 - \text{age}) \times \text{IBW} }{ 72 \times \text{Scr} } \times S $$Worked example
Take a 60-year-old man who is 175 cm tall with a serum creatinine of 1.0 mg/dL. His height is 175 divided by 2.54, which is about 68.9 inches, so his ideal body weight is 50 + 2.3 × (68.9 − 60), or roughly 70.5 kg. Plugging that into Cockcroft-Gault gives (140 − 60) × 70.5 / (72 × 1.0) = 5640 / 72, which is about 78.3 mL/min, placing him in the mild-reduction range.
Frequently asked questions
Why use ideal body weight instead of actual weight? In the Cockcroft-Gault equation, using actual weight in people with obesity can overestimate clearance because excess fat tissue adds little creatinine. Ideal body weight gives a more representative estimate; many references use IBW, or the actual weight when it is lower than IBW.
Which ideal body weight formula is used? The Devine formula: 50 kg for men (45.5 kg for women) plus 2.3 kg for every inch of height above 5 feet, which is 60 inches.
Is this the same as measured GFR? No. Cockcroft-Gault estimates creatinine clearance, which approximates kidney filtration but is not a direct measurement. It is not indexed to body surface area and should support, not replace, clinical judgement and lab-measured results.
