Creatinine Clearance Calculator — Cockcroft-Gault (CrCl)

Creatinine clearance is (140 − age) × weight in kg ÷ (72 × serum creatinine in mg/dL), multiplied by 0.85 for women. For a 70-year-old man weighing 80 kg with a creatinine of 1.2 mg/dL that comes to 64.8 mL/min. The part that trips people up is not the arithmetic — it is which weight to put in, because creatinine comes from muscle and the scale does not know the difference between muscle and fat. Enter the figures below and the calculator shows you the clearance, the weight it used and why it chose that one.

Created by Ashar PervaizMedically reviewed by Dr. Syeda Khadija AkbarLast reviewed 14 October 2026

Which Weight the Formula Wants

Cockcroft and Gault published their equation in 1976 from data on 249 men, and the weight in it was simply the weight of the patient. Obesity at the scale seen today was not in that sample, and the problem showed up later: creatinine is a breakdown product of muscle, so two people of the same weight, one muscular and one not, do not produce it at the same rate. Put the scale weight of a heavy patient into the equation and the answer comes out higher than their kidneys are really managing — which, for a drug cleared by the kidney, is the direction that causes harm.

The workaround that hospital pharmacy settled on is to feed the equation a weight that tracks muscle better than the scale does. There are three in common use, and this is the convention most units follow:

Ideal body weight here is the Devine formula — 50 kg for a man or 45.5 kg for a woman, plus 2.3 kg for every inch over five feet. Adjusted body weight is ideal plus 40% of the gap between actual and ideal. A 175 cm man has an ideal weight of 70.5 kg; if he actually weighs 110 kg, his adjusted weight is 86.3 kg, and that is the figure the equation should be given rather than 110.

Leave the selector on Auto and the calculator applies the table above, then tells you in the panel which weight it chose and on what grounds. Override it whenever your own protocol says otherwise — plenty of units have a house rule, and a calculator should not argue with one.

Creatinine Clearance and eGFR Are Not the Same Number

These two get used as synonyms and they are not. The lab report almost certainly says eGFR, calculated with CKD-EPI and reported in mL/min/1.73m². That last part matters: it has been normalised to a standard body surface area, so it describes kidney function per average-sized person rather than this particular person. It is the right number for staging chronic kidney disease, and it is the one nephrology works from.

What Cockcroft-Gault gives you is a plain mL/min figure for the patient in front of you, not normalised to anything. Most drug labels — particularly the older ones, and most renal dose adjustment tables — were written against this number, because it is what existed when those drugs were licensed. Substituting the lab's eGFR is tempting and usually close enough in an average-sized adult, but in someone very large or very small the two diverge sharply, and that is exactly the patient where a dosing error does damage.

The short version: stage kidney disease with eGFR, dose renally cleared drugs with whatever the label specifies, and if the label says creatinine clearance, calculate it rather than reading the eGFR off the report.

mg/dL and µmol/L

Creatinine is reported in mg/dL in the United States and in µmol/L across the UK, Ireland, Canada, Australia and New Zealand. The conversion is one number: 1 mg/dL = 88.4 µmol/L. A creatinine of 106 µmol/L is 1.2 mg/dL, and a creatinine of 1.0 mg/dL is 88.4 µmol/L.

You can skip the conversion by folding it into the equation. In µmol/L the formula becomes (140 − age) × weight × 1.23 for men, or × 1.04 for women, divided by the creatinine. Those two constants are just 88.4 ÷ 72 and the same again × 0.85. The calculator above converts internally rather than carrying two versions of the equation, which is how the two drift apart in a spreadsheet.

Reading the Result Against a Drug Label

The bands this page shows are the ones renal dosing tables are usually written around, and they are not the same as the five stages used for chronic kidney disease:

A figure near a cut-off deserves a second look rather than a decision. A patient calculating at 31 mL/min and one at 29 mL/min are clinically the same person, and the equation is not precise enough to separate them — but a dosing table will treat them differently. When the number lands within a few mL/min of a threshold, that is the moment to check the weight you used and whether the creatinine is a stable one.

The clearance figure is an input, not an answer. Once you have it, our dose calculator handles the mg/kg arithmetic the label then asks for, and the pharmacokinetics calculator covers what a reduced clearance does to half-life and to the time a drug takes to reach steady state.

Where the Estimate Breaks Down

Cockcroft-Gault assumes the creatinine it is given is at steady state. In acute kidney injury it is not: creatinine lags the damage by a day or more, so an early result in a deteriorating patient will read reassuringly normal while the kidneys are already failing. The equation cannot see that, and neither can this page.

It also assumes an adult producing creatinine at a fairly ordinary rate. Four groups break that assumption in a way worth knowing:

• Very low muscle mass — frail elderly patients, amputees, anyone with advanced liver disease or long-term immobility. Their creatinine is low because they make little of it, not because the kidney is clearing it well, so the estimate runs high.
• Very high muscle mass — the opposite error, and the reason a bodybuilder's creatinine can look alarming on an otherwise normal report.
• Rapidly changing function — anyone acutely unwell, where today's creatinine describes yesterday's kidney.
• Pregnancy — plasma volume and glomerular filtration both rise, and the equation was not derived in pregnant patients.

Some units round a creatinine below 0.6 mg/dL up to 1.0 before calculating, specifically to stop the first of those cases producing an implausible clearance in an 85-year-old. It is a long-standing practice and a contested one, and this calculator deliberately does not do it silently — it flags the low value and leaves the decision with you.

A Worked Example

A 70-year-old man, 80 kg, 175 cm, creatinine 1.2 mg/dL. His ideal body weight is 50 + 2.3 × (68.9 − 60) = 70.5 kg. His actual weight of 80 kg is 13.5% above that — inside 30%, so the convention says use ideal.

CrCl = (140 − 70) × 70.5 ÷ (72 × 1.2)
     = 70 × 70.5 ÷ 86.4
     = 4,935 ÷ 86.4
     = 57.1 mL/min

Had the calculation used his scale weight of 80 kg instead, it would have returned 64.8 mL/min. Both numbers sit in the 30–59 and 60–89 bands respectively — on opposite sides of a line that several drug labels care about. That single choice of weight is why this page makes you look at it.

Educational reference only. Confirm any clinical calculation independently before acting on it. How this page is reviewed