𧬠BSA Calculator
Body surface area by Du Bois, with Mosteller for comparison.
For education and planning. Clinical dosing must be verified by a pharmacist or clinician.
Body surface area is the size number medicine actually doses by. Chemotherapy, burn assessment, cardiac index, and renal function estimates all scale with BSA rather than weight, because metabolic processes track surface better than mass. The Du Bois formula from 1916 remains the reference standard; this calculator runs it and shows the simpler Mosteller formula alongside so you can see how closely they agree.
How to Use This Calculator
Enter height in centimeters and weight in kilograms. Both formulas compute instantly.
Enter height and weight. Use current, measured values rather than remembered ones.
Read the Du Bois BSA in square meters. Typical adults land between 1.6 and 2.2.
Check the Mosteller comparison. Agreement within a few percent is normal; large gaps suggest a data entry slip.
The Formulas
Du Bois and Du Bois derived their equation from measurements on just nine subjects, which sounds thin until you learn how well it has held up across a century of validation. The exponents capture the geometry: surface grows more slowly than weight, so the weight exponent (0.425) is smaller than the height exponent (0.725). Mosteller's 1987 simplification is beloved on wards because it can be done on a phone calculator: height times weight over 3600, square root. For typical adults the two agree within about 2 percent, which is why Mosteller dominates bedside use while Du Bois remains the publication standard.
Other formulas exist, Haycock, Gehan and George, Boyd, each fitted to different populations, mostly children. For adults they all cluster within a few percent of Du Bois. The choice of formula rarely changes a clinical decision; getting the weight right matters far more.
Worked Example
Height 178 cm, weight 82 kg. Du Bois: 0.007184 x 82^0.425 x 178^0.725 = 0.007184 x 6.508 x 42.83 = 2.00 m2. Mosteller: sqrt(178 x 82 / 3600) = sqrt(4.054) = 2.01 m2. The two agree within half a percent. A chemotherapy dose ordered at 100 mg per m2 becomes 200 mg; a cardiac output of 5.0 L/min divides by 2.00 to give a cardiac index of 2.5 L/min/m2, squarely normal. One number, three clinical uses, which is why BSA is worth knowing.
Where BSA Gets Used
Chemotherapy dosing is the flagship: most cytotoxic drugs are ordered per square meter because toxicity tracks BSA better than weight. Burn assessment uses BSA differently, estimating the percentage of skin burned (the rule of nines, the Lund-Browder chart) rather than total area. Cardiac index normalizes cardiac output to BSA so a 50 kg woman and a 100 kg man can be compared on the same scale. Renal drug dosing and dialysis adequacy use BSA-normalized values. If any of these touch your care, the BSA on this page is the same number your team computes, but dosing decisions always get verified by a pharmacist: this page educates, it does not prescribe.
For the curious: average adult BSA is about 1.9 m2 for men and 1.6 m2 for women in Western populations. Athletes and very tall people exceed 2.2. Children scale down dramatically, which is exactly why pediatric dosing leans on BSA instead of age-based fractions of adult doses. Our cardiac index calculator and carboplatin calculator both build on the number you just computed.
Accuracy and Limits
At extremes of obesity, BSA formulas overestimate metabolically active surface because fat adds area without proportional metabolic function; some protocols cap BSA at 2.0 or 2.2 m2 for chemotherapy for this reason. In severe edema or amputation, measured weight misleads the formula. And no formula replaces clinical judgment: BSA is an estimate of an estimate, useful because it beats every simpler alternative, not because it is exact. Enter honest numbers, note the Mosteller cross-check, and let the clinicians do the dosing.
For informational purposes only, not medical advice. Consult a healthcare professional.
Frequently Asked Questions
What is body surface area used for?
Chemotherapy dosing (most cytotoxic drugs are dosed per m2), burn size estimation, cardiac index calculation, and normalizing renal function. It predicts metabolic processes better than weight alone, which is why so much of medicine scales to it.
What is the Du Bois formula?
BSA = 0.007184 x weight(kg)^0.425 x height(cm)^0.725. Published by Du Bois and Du Bois in 1916 from direct measurements, it remains the reference standard despite being fitted to only nine subjects, because a century of validation has upheld it.
What is the Mosteller formula?
BSA = sqrt(height(cm) x weight(kg) / 3600). Published in 1987, it is the bedside favorite because it needs only a basic calculator. For typical adults it agrees with Du Bois within about 2 percent.
What is a normal BSA for adults?
Roughly 1.6 to 2.2 m2 for most adults, averaging about 1.9 for men and 1.6 for women in Western populations. Tall or large adults exceed 2.2; children are much smaller, which is why pediatric dosing uses BSA.
Why is chemotherapy dosed by BSA?
Because drug clearance and toxicity track body surface better than weight. Dosing per square meter keeps exposure consistent across body sizes. Some protocols cap BSA at 2.0-2.2 m2 in obesity to avoid overdosing.
How accurate is the Du Bois formula?
Within a few percent for typical adults versus direct measurement. Accuracy softens at extremes of obesity, where fat adds surface without proportional metabolic function, and with edema or amputations that distort weight.
Which BSA formula should I use?
Du Bois for publication and precision, Mosteller for bedside speed. For adults the difference rarely matters clinically. Pediatric practice sometimes prefers Haycock. When in doubt, match whatever formula your institution uses.
Can I calculate BSA in inches and pounds?
Yes, but convert first: the standard formulas take cm and kg. Convert inches to cm (x 2.54) and pounds to kg (x 0.4536), then apply Du Bois or Mosteller. This calculator accepts cm and kg directly.
What is the rule of nines in burns?
A method for estimating burn size as a percentage of BSA: each major body region is about 9 percent (or a multiple). It estimates burned percentage of skin, which is different from the total BSA this calculator computes, but both use the body-surface concept.
Does BSA change with weight loss?
Yes, since weight is in the formula. Losing 10 kg drops BSA by roughly 0.1 m2 for a typical adult. That is why chemotherapy doses get recalculated when weight changes significantly during treatment.