Body Surface Area (BSA) is widely used in medicine - chemotherapy and many drug doses are calculated per square metre of BSA, and burn assessment uses surface area percentages. This calculator returns BSA from three classic formulas: Mosteller, DuBois and Haycock.
Mosteller (modern)
1.82 m²
Most common in oncology
DuBois
1.81 m²
Historical reference
Haycock
1.83 m²
Preferred for paediatrics
Why BSA matters
Chemotherapy is dosed mg per m² of BSA. GFR is normalised to 1.73 m² (the average adult BSA). Burn assessments use % of total BSA burned - the Rule of Nines is a clinical shortcut.
Different formulas can disagree by up to 5% - most clinicians stick to one (Mosteller in adults, Haycock in children) for consistency. For very obese patients, BSA may be capped (often at 2.0 m²) when dosing chemotherapy to avoid toxicity.
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Body Surface Area (BSA) is a critical clinical measurement used across oncology, burn care, pediatric medicine, cardiology, and many drug-dosing protocols. Many medications - especially chemotherapy agents - are dosed in milligrams per square metre of BSA, because BSA correlates with metabolic rate and drug distribution volume more accurately than weight alone. A 60 kg child and an 80 kg adult might both need the same dose for some drugs, while differing dramatically for others - BSA helps standardise dosing across body sizes.
This calculator computes BSA using the three most-cited formulas: Mosteller (the modern clinical standard for adults), DuBois (the historical reference), and Haycock (preferred for pediatric calculations). All three are accurate within 3% of each other for normal-range adults; differences become meaningful at extremes (very thin, very obese, or very young patients). The output is in square metres - typical adult BSA is 1.6-2.0 m², pediatric ranges from 0.2 m² (newborn) to 1.5 m² (adolescent).
Enter weight in kg and height in cm.
Read BSA from each formula - most clinical settings use Mosteller for its simplicity.
Mosteller is the simplest: BSA = √(weight × height / 3600). DuBois uses fractional powers calibrated to historic clinical data. Haycock is preferred for paediatrics. All three return values in m².
Mosteller: √(W × H / 3600) DuBois: 0.007184 × W^0.425 × H^0.725 Haycock: 0.024265 × W^0.5378 × H^0.3964
Mosteller formula (the modern standard for adult clinical use): BSA = √(weight × height / 3600). Simple, accurate, easy to compute mentally. DuBois formula (1916, historic reference): BSA = 0.007184 × W^0.425 × H^0.725. Calibrated against direct surface area measurements of nine subjects (small sample, hence its limitations at extremes). Haycock formula (1978, pediatric preferred): BSA = 0.024265 × W^0.5378 × H^0.3964. Validated on a larger pediatric population.
Clinical applications of BSA: Chemotherapy dosing (most agents specified in mg/m²), pediatric drug dosing (where adult dosing rules don't apply), cardiac index (cardiac output normalised to BSA, used in heart-failure assessment), burn severity (% Total Body Surface Area burned guides fluid resuscitation), renal clearance normalization (eGFR per 1.73m²), and intravenous fluid calculations.
Limitations: BSA overestimates surface area in extreme obesity (BMI 40+) and can lead to chemotherapy toxicity if used naively. Many oncology protocols cap BSA at 2.0 m² for dose calculation to limit drug exposure. For pediatric calculations, Haycock or Mosteller should be used; older formulas (Boyd's table) are less accurate. Even with the right formula, BSA estimates are within ±5% of measured surface area - sufficient for clinical dosing but not exact.
Mosteller: √(75 × 175 / 3600) = √(13125/3600) = √3.65 = 1.91 m². DuBois: 0.007184 × 75^0.425 × 175^0.725 ≈ 1.89 m². Haycock: 0.024265 × 75^0.5378 × 175^0.3964 ≈ 1.92 m². Average ≈ 1.91 m². All three formulas agree within 1.5% for this normal-range adult.
Mosteller: √(25 × 125 / 3600) = √0.868 = 0.93 m². Haycock: 0.024265 × 25^0.5378 × 125^0.3964 ≈ 0.95 m². Use Haycock for pediatric drug calculations. The 0.02 m² difference is small but matters for narrow-therapeutic-index drugs.
Each was derived from different population samples and slightly different methodologies. Differences are small - usually <3% between formulas - but matter for chemotherapy dosing where precision counts.
Mosteller is the most common in modern oncology because it's simple and accurate. DuBois is the historical reference. Haycock is favoured in paediatrics.
Average adult: 1.6-2.0 m². Children: much lower (0.5-1.0 m²). Used as a denominator for body-size-adjusted dosing.
Most chemotherapy doses are mg per m² of BSA. A drug dosed at 100 mg/m² gives 180 mg to a patient with 1.8 m² BSA. This standardises dosing across body sizes.
Yes - burn severity uses % of total body surface area burned (TBSA). A '20% burn' means 20% of the patient's BSA. The Rule of Nines is a quick clinical estimation.
Less well - it overestimates BSA in extreme obesity. Modified formulas or capped BSA (often capped at 2.0 m²) are used for chemo dosing in obese patients to avoid toxicity.
Body composition, daily energy needs and pregnancy timelines all rest on formulas validated across millions of people, but no single number tells the whole story. The values from this calculator are point estimates with a known margin of error - body fat from skinfold or US Navy method has roughly a ±3% standard error compared to a DEXA scan, and BMR can vary ±10% person to person at the same height and weight. Use these numbers to track trends week over week, not to chase decimal precision day to day.
Pair this tool with the BMR, TDEE, calorie and macro calculators to turn a single measurement into an actionable plan. None of these tools are a substitute for a qualified doctor, registered dietitian or certified strength coach - but they remove the busywork so you spend more time on training and recovery, less on math.
The Body Surface Area Calculator is part of the Health & Fitness suite on Online Calculator Tools, alongside 6 related calculators. All tools share the same UI patterns, the same privacy-first rendering (nothing is sent to a server), and the same commitment to showing the formula and assumptions behind every result.
