Optional — needed for adjusted body weight, BMI and the recommendation
Ideal body weightConventional
73.2 kg
Adjusted body weight
73.9 kg
Actual body weight
75.0 kg
BMI: 23.7 kg/m²
Actual weight is 102% of ideal body weight and BMI is 23.7 kg/m², so ideal body weight is conventionally used.
Weight-basis selection is a dosing convention, not a validated equation. Institutional protocol and a drug’s prescribing information override it.
Updates as you type · no submit
Use ideal body weight for most patients, adjusted body weight when the patient is obese, and actual body weight when it falls below ideal. Ideal body weight comes from the Devine formula and adjusted body weight from Bauer. These are dosing conventions rather than validated equations — the original Cockcroft-Gault paper used actual weight — so institutional protocol overrides them.
Why it matters
Cockcroft-Gault multiplies by body weight because weight stands in for muscle mass, and muscle mass is what produces creatinine. Adipose tissue produces very little. So in a patient carrying a large amount of fat, feeding actual weight into the equation credits them with muscle they do not have and overestimates clearance — which, for a renally cleared drug with a narrow margin, means a dose that is too high.
Ideal body weight corrects that by estimating what the patient would weigh at a healthy build for their height. Adjusted body weight sits between the two, on the reasoning that fat tissue is not metabolically inert and contributes something. Which one applies is a decision, and this page exists to make that decision visible rather than silent.
The formulas
Both are simple arithmetic and both are reproduced here exactly as published, so you can check this calculator against them rather than trust it.
Male: IBW (kg) = 50.0 + 2.3 × (height in inches − 60) Female: IBW (kg) = 45.5 + 2.3 × (height in inches − 60)
Source: Devine BJ. Drug Intell Clin Pharm. 1974;8:650–5.
AdjBW (kg) = IBW + 0.4 × (actual weight − IBW) 0.4 = proportion of weight above ideal that is counted
Source: Bauer LA et al. Clin Pharmacol Ther. 1983;33(4):519–25.
Choosing
The thresholds below are the conventional ones. They are not from a trial, and they are not a rule you are obliged to follow — they describe what most renal dosing references do. The calculator marks the conventional choice and still shows you all three.
| Situation | Weight used | Why |
|---|---|---|
| Actual weight below ideal < IBW | Actual body weight | Using ideal body weight here would credit the patient with muscle they do not have and overestimate clearance. |
| Normal build ≤ 120% of IBW and BMI < 30 | Ideal body weight | The conventional default, and the basis most renal dosing references assume unless they say otherwise. |
| Obese by BMI ≥ 30 kg/m² | Adjusted body weight | Actual weight would substantially overestimate clearance; ideal weight alone would ignore the real metabolic contribution of the excess tissue. |
| Well above ideal without meeting the BMI cut-off > 120% of IBW | Adjusted body weight | A muscular or large-framed patient can exceed ideal weight considerably without a BMI in the obese range; the adjustment still applies. |
Worked examples
Every figure below is computed by the same code that runs the calculator above, so if one changes the other changes with it.
Male, 178 cm, 75 kg
178 cm = 70.1 inches
IBW = 50.0 + 2.3 × (70.1 − 60)
= 50.0 + 2.3 × 10.1 = 73.2 kg
BMI = 75 / 1.78² = 23.7 kg/m²
Actual 75 kg = 102% of IBW → ideal body weight73.2kg
Actual weight is close to ideal, so the conventional choice is ideal body weight and the two answers barely differ.
Male, 178 cm, 130 kg
178 cm = 70.1 inches
IBW = 73.2 kg (as above — height and sex only)
BMI = 130 / 1.78² = 41.0 kg/m² → obese
AdjBW = 73.2 + 0.4 × (130 − 73.2)
= 73.2 + 22.7 = 95.9 kg95.9kg
Here the choice matters most. Actual weight would nearly double the clearance estimate against ideal weight — the single largest source of error in a Cockcroft-Gault result.
Female, 160 cm, 44 kg
160 cm = 63.0 inches
IBW = 45.5 + 2.3 × (63.0 − 60)
= 45.5 + 6.9 = 52.4 kg
Actual 44 kg is below IBW 52.4 kg
→ actual body weight is used44.0kg
Actual weight is below ideal, so ideal body weight is not used. Applying it anyway would overestimate clearance in exactly the patient least able to tolerate an overdose.
Limitations
Devine was never derived from a study of body composition. It was written in 1974 as a rule of thumb for dosing, and it has been used far beyond that ever since. Knowing where it stops being reasonable matters more than the arithmetic.
The formula subtracts a fixed amount per inch under 60, so a short patient gets an ideal weight that keeps falling in a straight line. The calculator flags a result as extrapolated rather than presenting it as though the formula were validated there.
A bodybuilder and a sedentary patient of the same height and sex get the same ideal body weight. Muscle mass is what actually drives creatinine production, and height is a poor proxy for it at the extremes.
Devine assumes an adult frame and should not be applied to paediatric patients. Use the bedside Schwartz equation instead.
Ideal body weight is derived from height, and an amputation removes mass without changing height. The special populations calculator applies the limb-segment correction.
Questions
The questions that come up most often when choosing a weight basis. Every answer states its source.
Devine (1974): ideal body weight in kg = 50.0 for men or 45.5 for women, plus 2.3 kg for every inch of height above 60. Height is converted to inches first. Ideal body weight therefore depends only on height and sex — two patients of the same height and sex have the same ideal body weight whatever they actually weigh.
Ideal body weight for most patients, adjusted body weight when the patient is obese, and actual body weight when actual falls below ideal. This is a dosing convention rather than a validated equation — the original 1976 Cockcroft-Gault paper used actual weight — so institutional protocol and a drug’s prescribing information override it.
Adjusted body weight = ideal body weight + 0.4 × (actual weight − ideal body weight), from Bauer et al. (1983). It is conventionally used when BMI is 30 kg/m² or above, or when actual weight exceeds 120% of ideal. It sits between actual and ideal because adipose tissue produces some creatinine, but far less per kilogram than muscle.
Cockcroft-Gault multiplies by weight because weight stands in for muscle mass, and muscle is what produces creatinine. Adipose tissue produces very little, so actual weight credits an obese patient with muscle they do not have and overestimates clearance — which for a renally cleared drug with a narrow margin means a dose that is too high.
No. Below 60 inches the formula keeps subtracting 2.3 kg per inch in a straight line, well outside the range it was written for, and can return implausibly low values. Treat the result as an estimate, check it against institutional guidance, and note that Devine was never derived from a study of body composition — it was published in 1974 as a dosing rule of thumb.
More calculators
This page gives you the weight. These calculators use it — the main Cockcroft-Gault tool shows all three bases side by side automatically.
Standard adult creatinine clearance with actual, ideal and adjusted body weight side by side.
Open calculatorCKD-EPI 2021 creatinine, cystatin C and combined equations, plus Schwartz for children and a CrCl comparison.
Open calculatorWeight-basis selection, Salazar-Corcoran, amputation correction, paediatric equations and mL/hour output.
Open calculatorMeasured clearance from a timed collection, with a collection-adequacy check and BSA normalisation.
Open calculatorEvery calculator on this site is free, needs no account, and runs entirely in your browser.
Security & privacy
All calculations run entirely in your browser. No patient values are transmitted, logged or stored.
The equations run as JavaScript on your device. There is no API endpoint that accepts a clinical value, because the calculation code never makes a network request.
Values are not written to a database, a log, local storage or a cookie. Closing the tab discards them.
No signup, no email capture, no paywall. Every calculator works fully without identifying yourself.
Google Analytics counts page views. It runs outside the calculator, receives nothing you type, and has ad personalisation switched off. No advertising network, no embedded widgets, no remote fonts.
This is a property of how the site is built, not a policy that could quietly change. Read the full privacy policy or the terms and medical disclaimer.
Get in touch
Clinical corrections take priority over everything else on this site. If an equation, threshold or caveat here is wrong, we want to hear about it.
Tell us the page, what is incorrect, and a source if you have one. Please do not include any patient information.
Email a correctionMore ways to reach us →We publish guest guides from pharmacists, prescribers, nurses and clinical educators — with a real byline and a link back to your work.
See the guidelinesRead the existing guides →This site is built and maintained by Gem Programmers. If you need a calculator, a technical-SEO build or a content programme of your own, talk to us.
Message on WhatsAppAbout Ali Raza →The main CrCl calculator applies all three weight bases at once and marks the conventional choice, so you never have to copy a number between pages.
Medical disclaimer: This calculator is intended for healthcare professional reference and educational purposes only. It does not replace clinical judgment or the advice of a licensed provider. Always verify dosing decisions against institutional protocol and current prescribing information.