Audited —·Last updated 27 Jul 2026·7 citations·Tier 1·0 uses

Body Surface Area (BSA) Calculator

Free BSA calculator with Mosteller, Du Bois, Haycock, Boyd, and Gehan-George formulas — clinical body surface area in m² for chemo dosing and cardiac index.

Body Surface Area Calculator

Weight unit
Height unit
Formula
Body Surface Area (selected formula)
1.8181
Body Surface Area (imperial)
19.57 ft²
Mosteller BSA
1.8181 m²
Du Bois BSA
1.8097 m²
Haycock BSA
1.8257 m²
Boyd BSA
1.8347 m²
Gehan-George BSA
1.8313 m²

Background.

This body surface area calculator computes BSA in m² using all five clinically accepted formulas — Mosteller, Du Bois & Du Bois, Haycock, Boyd, and Gehan-George — from a single height and weight pair, so you can dose, scale, and index without flipping between references. BSA is the two-dimensional measure of the human body's outer envelope, and despite being a less intuitive quantity than weight or BMI, it remains the single most important scaling variable in adult oncology, pediatric medicine, critical care, burn surgery, and cardiology. Drug clearance, glomerular filtration, basal metabolic rate, cardiac output, and blood volume all scale more tightly with BSA than with mass alone, because surface area tracks heat-exchange capacity and organ size better than weight does in heterogeneous populations. That is why chemotherapy protocols since the 1950s have specified doses in mg/m² rather than mg/kg, why echocardiographers report cardiac index in L/min/m² rather than raw cardiac output, why pediatric fluid resuscitation in major burns is driven off m² of body and m² of burn, and why GFR results are still normalized to 1.73 m² — the average BSA of a young adult in the 1920s.

The reason this tool returns five numbers instead of one is that no single regression equation is correct everywhere on the human size spectrum. Du Bois & Du Bois published the original formula in 1916 after physically wrapping just nine cadavers and live subjects in paper to trace their surface — a heroic study for its time, but its sample was small, lean, and adult, and it under-predicts BSA in obese patients and in infants. Haycock and colleagues re-derived the relationship in 1978 specifically to fix the pediatric drift, validating their fit in 81 subjects spanning neonates to adults. Boyd's 1935 monograph used a much larger sample of children and adults but introduced an exponent on weight that itself depends on weight (via a log term), making it more accurate at extremes but harder to compute mentally. Gehan and George produced their formula in 1970 from 401 direct measurements at the M.D. Anderson Hospital, expressly for chemotherapy dosing. Then in 1987 Mosteller published the now-dominant simplified form BSA = √(height × weight / 3600), which is within ~2% of Du Bois across normal adults, can be computed on a bedside calculator, and has become the de facto standard in clinical pharmacy.

By showing you all five values side by side, this tool lets you see how much the BSA estimate moves as a function of formula choice — typically less than 5% in average-size adults, but up to 10–15% in very small infants or morbidly obese patients, which is exactly the population in which the formula choice starts to matter clinically. For chemotherapy, ICU drug infusions, contrast dose limits, renal clearance scaling, and cardiac index, the resulting m² is the input you feed downstream. Quanta's engine does the conversion from pounds and inches to kg and cm using NIST SP 811 exact factors and runs every calculation at full Decimal precision, so unit conversion never introduces a second source of rounding on top of the formula choice itself.

What is body surface area calculator?

Body surface area (BSA) is the calculated total surface of the human body, expressed in square meters (m²) and historically derived from height and weight via regression equations fitted to direct anatomical measurements. It is used clinically as a normalization variable: many drugs, fluid volumes, and physiological flows scale more accurately with surface area than with body mass, because surface area better reflects organ size, metabolic rate, and heat exchange. Adult BSA typically falls between 1.5 and 2.0 m²; neonates start near 0.25 m². The five standard formulas — Mosteller (1987), Du Bois & Du Bois (1916), Haycock (1978), Boyd (1935), and Gehan-George (1970) — agree to within a few percent for average adults but diverge at the extremes of size, which is why the formula choice is itself a clinical decision.

How to use this calculator.

  1. Enter the patient's weight and choose kilograms or pounds.
  2. Enter the patient's height and choose centimeters or inches.
  3. Select which BSA formula should drive the primary m² output — Mosteller is the standard default for adult inpatient pharmacy.
  4. Read the primary BSA (m² and ft²) at the top of the results panel.
  5. Compare the four other formulas in the breakdown to see how much the estimate moves with formula choice — meaningful divergence (>5%) usually signals a pediatric, geriatric, or obese patient where formula selection matters.
  6. Feed the m² value into your downstream calculation (chemo dose, cardiac index, GFR normalization, burn fluid volume).
  7. Document the formula used alongside the BSA in the medical record — protocols often specify which formula must be applied.

The formula.

BSA = √(cm × kg ⁄ 3600)
BSA · body surface area in m²cm · height in centimetreskg · weight in kilograms3600 · Mosteller constantDu Bois · 0.007184 × kg^0.425 × cm^0.725

Mosteller (1987): BSA = √(height_cm × weight_kg ÷ 3600). The simplest of the five — a single multiplication, division, and square root. It approximates Du Bois closely in normal-range adults and is the formula most U.S. and U.K. hospital pharmacies cite for chemotherapy dosing. Du Bois & Du Bois (1916): BSA = 0.007184 × W^0.425 × H^0.725, with weight in kg and height in cm. The original allometric fit; its small derivation sample (n=9) explains why it drifts at the extremes. Haycock, Schwartz & Wisotsky (1978): BSA = 0.024265 × W^0.5378 × H^0.3964. Re-fit on 81 subjects from neonates to adults specifically to remove the pediatric bias in Du Bois. Boyd (1935): BSA = 0.0003207 × H^0.3 × W_g^(0.7285 − 0.0188·log₁₀ W_g), where W_g is weight in grams. The weight exponent is itself a function of weight, giving Boyd unusual robustness across the wide pediatric-to-bariatric range, at the cost of arithmetic complexity. Gehan & George (1970): BSA = 0.0235 × W^0.51456 × H^0.42246. Derived from 401 direct measurements at M.D. Anderson and historically favored in U.S. oncology trials. All five return BSA in m². The engine also returns the primary result converted to ft² using the NIST exact factor 1 m² = 10.7639 ft².

A worked example.

Example

Take a 70 kg patient who is 170 cm tall and apply Mosteller. The product of height and weight is 170 × 70 = 11,900. Dividing by 3,600 gives 3.3056. The square root of 3.3056 is 1.8181, so the Mosteller BSA is 1.82 m² (about 19.57 ft²). Running the same height and weight through the other four formulas returns 1.81 m² for Du Bois, 1.83 m² for Haycock, 1.82 m² for Boyd, and 1.83 m² for Gehan-George. All five agree within 0.02 m², which is typical for an average-size adult and is why Mosteller's bedside-friendly square root has become the default. For a chemotherapy protocol specifying 75 mg/m² of doxorubicin, this patient would receive 75 × 1.82 = 136.5 mg, rounded to the nearest 5 mg per institutional policy. For cardiac index, a measured cardiac output of 5.0 L/min divided by the BSA of 1.82 m² gives a cardiac index of 2.75 L/min/m² — within the normal 2.5–4.0 range.

formulamosteller
weight70
height170

Frequently asked questions.

Which BSA formula should I use clinically?
For adult inpatient pharmacy and most chemotherapy protocols, Mosteller is the default because it is the simplest to verify by hand and matches Du Bois within ~2% across normal adults. Haycock is preferred for pediatric patients, especially infants under one year, because it was specifically re-derived to fix Du Bois's pediatric drift. Boyd is the best single choice when you need one formula to span both extremes (premature neonates and morbidly obese adults). Always document which formula was used — many oncology trial protocols specify Du Bois or Gehan-George by name, and substituting another can change the dose by a clinically meaningful amount.
Why is Mosteller's formula so dominant in clinical practice?
Mosteller published his simplified form in a 1987 letter to the New England Journal of Medicine, showing that BSA = √(height × weight ÷ 3600) tracks Du Bois to within 2% for the great majority of patients while being computable on any bedside calculator without an exponent key. Before pocket calculators with power functions were universal, computing W^0.425 × H^0.725 at the bedside was painful, so a formula needing only a multiplication, a division, and a square root was an enormous workflow improvement. The simplicity also makes pharmacy double-checks faster and reduces transcription errors, which is why hospital pharmacy and electronic prescribing systems standardized on it.
Why is the Du Bois formula still cited if it was derived from only nine subjects?
Du Bois & Du Bois published their formula in 1916 in the Archives of Internal Medicine after wrapping just nine subjects (including one cadaver and an infant) in paper molds to measure their surface area directly. Although the sample was tiny, it became the foundation for almost a century of clinical scaling work because nothing better was published for decades, and because in average adults it agrees with later, larger studies within a few percent. It under-predicts BSA in obese patients (where folds and surface curvature are not captured) and in infants, but its historical primacy means many older oncology and pharmacokinetic studies report doses normalized to Du Bois BSA, and protocols built on those studies still specify it by name.
Why do many oncology protocols cap chemotherapy BSA at 2.0 or 2.2 m²?
Almost all of the pharmacokinetic studies that established the safe and effective mg/m² doses of older cytotoxic agents enrolled patients with BSA below 2.0 m². Extrapolating linearly beyond that range risks overdosing very large patients, because drug clearance does not scale infinitely with body size. Many institutional protocols therefore cap the dosing BSA at 2.0 or 2.2 m² — known as 'BSA capping' — even when the patient's calculated BSA is higher. ASCO's 2012 guideline on obese cancer patients explicitly recommended against routine BSA capping for most curative-intent regimens, on the grounds that under-dosing harms outcomes, but capping remains common for palliative regimens and for drugs with narrow therapeutic indices.
Should BSA be calculated from actual or ideal body weight?
For most clinical purposes — chemotherapy dosing, cardiac index, GFR normalization — BSA is calculated from actual body weight, because the regression equations themselves were fitted to actual measurements. Using ideal body weight would systematically under-estimate BSA in obese patients. The exception is some hydrophilic drugs whose volume of distribution does not increase proportionally with adipose tissue — these are often dosed on adjusted body weight or on lean body weight rather than on BSA at all. When BSA is normalized to a reference (such as GFR per 1.73 m²), the patient's actual BSA is used in the numerator.
How accurate is BSA from a height-weight formula compared to direct measurement?
Direct 3D laser scanning of the human body yields BSA values that agree with Mosteller and Du Bois to within roughly ±5% in average-size adults, which is well inside the noise of clinical dosing. The error grows at the extremes — premature neonates and patients with BMI > 40 can show 10–15% disagreement between formulas, and between any formula and direct measurement. This is the strongest argument for showing all five values: when they cluster tightly, you can trust any one of them; when they disagree by more than 5%, the patient is at the edge of the population the formulas were fitted to, and formula choice has become a clinical decision.
Why is GFR reported per 1.73 m² specifically?
Glomerular filtration rate is conventionally normalized to a BSA of 1.73 m² — the average BSA of a 25-year-old American adult in the 1920s, taken from a 1928 paper by McIntosh, Möller and Van Slyke. The convention stuck because it lets clinicians compare a child's GFR to an adult reference range without separate pediatric tables. Modern guidelines from KDIGO continue to report estimated GFR (eGFR) per 1.73 m² as the primary number, with the patient's actual BSA used only when dosing renally cleared drugs in patients whose body size differs substantially from the reference.
What is the lean body weight versus BSA dosing trend in oncology?
Over the past 15 years, several pharmacokinetic studies have shown that lean body weight or lean BSA predicts cytotoxic drug clearance better than total BSA, particularly in obese patients and women with high body-fat fractions. Drugs including docetaxel, paclitaxel, and 5-fluorouracil have been studied under lean-weight dosing, and some trial protocols now use lean body weight directly. Total BSA remains the regulatory standard on the label for almost all cytotoxic agents, so lean-weight dosing is still a research and institutional-protocol decision rather than a universal replacement. The five formulas in this calculator all return total BSA; lean BSA would require a separate body-composition model.
What BSA values are normal at different ages?
A term neonate has a BSA near 0.25 m². At one year, BSA is roughly 0.45 m². At ten years, around 1.1 m². A typical adult woman is 1.6–1.8 m² and a typical adult man is 1.9–2.1 m². BSA above 2.5 m² is unusual and is typically seen only in very tall or obese patients. Because BSA is the variable that drives drug dosing for most cytotoxic agents, pediatric oncologists use age-appropriate nomograms in addition to the Haycock or Mosteller formula to sanity-check the calculated value before prescribing.
Can I use this calculator for veterinary BSA?
No. The five formulas implemented here were all derived from direct measurements of humans, and the regression constants are not transferable to other species. Veterinary BSA is usually computed from species-specific equations — for example, the canine formula BSA = 0.101 × W_kg^(2/3) used in veterinary oncology. Using a human formula on a dog or cat will systematically under- or over-estimate BSA and could result in unsafe chemotherapy dosing.

References& sources.

  1. [1]Mosteller RD. Simplified calculation of body-surface area. N Engl J Med. 1987;317(17):1098. — Original publication of the dominant clinical BSA formula.
  2. [2]Du Bois D, Du Bois EF. A formula to estimate the approximate surface area if height and weight be known. Arch Intern Med. 1916;17:863–871. — The original BSA regression, derived from nine subjects.
  3. [3]Haycock GB, Schwartz GJ, Wisotsky DH. Geometric method for measuring body surface area: a height-weight formula validated in infants, children, and adults. J Pediatr. 1978;93(1):62–66. — Pediatric-validated BSA formula.
  4. [4]Boyd E. The Growth of the Surface Area of the Human Body. Minneapolis: University of Minnesota Press; 1935. — Boyd's full monograph deriving the variable-exponent BSA formula across a wide age and weight range.
  5. [5]Gehan EA, George SL. Estimation of human body surface area from height and weight. Cancer Chemother Rep. 1970;54(4):225–235. — BSA formula derived from 401 direct measurements at M.D. Anderson, historically used in U.S. oncology trials.
  6. [6]Griggs JJ, et al. Appropriate Chemotherapy Dosing for Obese Adult Patients With Cancer: ASCO Clinical Practice Guideline Update. J Clin Oncol. 2021;39(18):2037–2048. — Current ASCO guidance on BSA-based dosing and BSA capping in obese cancer patients.
  7. [7]Levey AS, et al. KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease. Kidney Int. 2024;105(4S):S117–S314. — Reference for GFR normalization to 1.73 m² BSA.
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