What is creatinine clearance?
Creatinine is a waste product from normal muscle activity. Healthy kidneys filter it out of the blood. Creatinine clearance is an estimate of how much blood plasma the kidneys clear of creatinine per minute, shown in mL/min.
The Cockcroft-Gault equation is a long-standing way to estimate it from age, weight, sex and a blood creatinine level. It has traditionally been used in drug dosing references.
How to calculate it manually
- Subtract your age from 140.
- Multiply by weight in kilograms.
- Multiply serum creatinine (mg/dL) by 72.
- Divide the first result by the second.
- If female, multiply by 0.85.
If your lab reports creatinine in umol/L, divide by 88.4 to convert to mg/dL first.
Which weight should I use?
The original equation used actual body weight. When someone is much heavier or lighter than their ideal weight, references sometimes suggest other choices.
- Actual weight: the plain version of the equation.
- Ideal body weight (Devine): based on height and sex, using 50 kg (male) or 45.5 kg (female) plus 2.3 kg per inch over 5 feet.
- Adjusted body weight: ideal weight plus 40% of the extra weight above ideal, sometimes used when actual weight is well over ideal.
The right choice depends on the situation, and a pharmacist or clinician can tell you which one applies. This calculator lets you see all three side by side by switching the selection.
CrCl is not the same as eGFR
Estimated GFR (eGFR) comes from different equations, such as CKD-EPI, and is the number normally used to stage kidney function. Cockcroft-Gault gives a creatinine clearance in mL/min and is not adjusted for body surface area. The numbers can differ, sometimes by a lot.
This tool does not give an eGFR and does not stage or diagnose kidney disease. If you are worried about your kidneys, a clinician can order the right tests.
Why drug dosing uses it
Many medicines are cleared by the kidneys, so the dose may need adjusting when clearance is lower. Some drug labels still list dosing in terms of Cockcroft-Gault creatinine clearance for this reason. Dose decisions should always come from a clinician or pharmacist, who also considers the medicine, your condition and other factors.
Limits of the formula
- It assumes stable kidney function. It is unreliable when creatinine is changing quickly, such as in acute illness.
- Very low or very high muscle mass, amputations, and extreme body sizes reduce accuracy.
- Creatinine itself is affected by diet, supplements such as creatine, and some medicines.
- It was developed in adults and is not intended for children.
Typical creatinine units
US labs usually report creatinine in mg/dL, while many other countries use umol/L. Divide umol/L by 88.4 to get mg/dL. For example, 106 umol/L is about 1.2 mg/dL. Choose the matching unit above so the calculator converts it for you.