Calculate body surface area with the Mosteller, Du Bois, Haycock and Gehan formulas, plus the total dose when a dose is given per square metre.
kg
cm
mg/m²
For example chemotherapy doses. Leave empty if you do not need it.
Enter the values to see the result here.
Calculation aids only. They do not replace clinical judgement or the drug reference. Verify every dose before using it on a patient.
Formula
The Mosteller formula, with weight W in kilograms and height H in centimetres:
BSA=3600H×W
Du Bois uses 0.007184W0.425H0.725, Haycock uses 0.024265W0.5378H0.3964 and Gehan and George use 0.0235W0.51456H0.42246. All give the area in square metres.
Worked example
A patient weighs 70 kg and is 175 cm tall.
Product: 175×70=12250.
Divide by 3600: 3.4028.
Square root: 1.84m2.
A drug prescribed at 75 mg/m² then comes to 75×1.84=138 mg.
Common mistakes
Entering height in metres or weight in pounds. This tool expects centimetres and kilograms.
Mixing formulas between the prescriber and the pharmacy. Two formulas can differ by 0.05 m² or more in children.
Forgetting a local cap on BSA for very large patients.
Rounding the BSA too early. Keep two decimals, then round the final dose.
Frequently asked questions
Which body surface area formula should I use?
Mosteller is the most widely used because it is simple and accurate for adults and children. Du Bois is the historical standard. Haycock and Gehan and George were fitted to infants and children. Follow the formula named in your drug protocol, since doses were validated against it.
Why is BSA used to dose some drugs?
Cardiac output, kidney function and drug clearance track body surface area better than raw weight. That is why chemotherapy, some antibiotics and cardiac indices are dosed per square metre.
Should I use actual or ideal weight?
Most protocols use actual weight, but some cap the BSA at 2.0 m² or use an adjusted weight in obesity. Check the local policy before dosing.