Body Surface Area (BSA) Calculator

Body Surface Area (BSA) Calculator for Endocrinology. Adult BSA typically falls between 1.5 and 2.0 m², with 1.73 m² historically used as the "standard" reference (the origin of eGFR normalization to 1.73 m²). Values are used as a multiplier, not a risk band: a higher BSA proportionally raises absolute chemotherapy dose and lowers indexed cardiac/valve measurements. Because obese patients accrue disproportionately large calculated BSA, many oncology protocols cap dosing BSA at 2.0–2.2 m² or use adjusted/ideal body weight to avoid overdosing; conversely, indexing to BSA can mask relative under-sizing of the heart in obesity.

How this calculator works

BSA estimates the two-dimensional external area of the body (in m²) from height and weight using an empirically fitted power equation. The most common is Mosteller: BSA = square root of [(height in cm × weight in kg) / 3600], which reduces to √(cm·kg)/60. The older Du Bois equation is BSA = 0.007184 × height(cm)^0.725 × weight(kg)^0.425, and pediatric-favored alternatives include Haycock (0.024265 × ht^0.3964 × wt^0.5378), Gehan-George, and Boyd. All are regression fits to a small number of directly measured cadaver/coating surfaces, not physiological measurements.

When to use this calculator

Use BSA to normalize physiologic and pharmacologic quantities to body size: cytotoxic chemotherapy dosing (mg/m²), cardiac index (cardiac output/BSA), indexed echocardiographic and valve-area measurements, glucocorticoid and some pediatric drug dosing, and estimating maintenance fluids. It is the standard denominator in oncology and cardiology. BSA is NOT a nutritional or adiposity measure (use BMI for that), and mg/m² dosing is discouraged for many biologics and targeted agents that use flat or weight-based dosing.

Inputs used

  • Height
  • Weight

Clinical interpretation

Adult BSA typically falls between 1.5 and 2.0 m², with 1.73 m² historically used as the "standard" reference (the origin of eGFR normalization to 1.73 m²). Values are used as a multiplier, not a risk band: a higher BSA proportionally raises absolute chemotherapy dose and lowers indexed cardiac/valve measurements. Because obese patients accrue disproportionately large calculated BSA, many oncology protocols cap dosing BSA at 2.0–2.2 m² or use adjusted/ideal body weight to avoid overdosing; conversely, indexing to BSA can mask relative under-sizing of the heart in obesity.

Worked example

A 170 cm, 70 kg adult by Mosteller: (170 × 70) = 11,900; 11,900 / 3600 = 3.306; √3.306 = 1.82 m². Du Bois for the same patient gives 0.007184 × 170^0.725 × 70^0.425 = ~1.81 m², a difference under 1%. If carboplatin-style or anthracycline dosing is 75 mg/m², this patient receives roughly 75 × 1.82 = 137 mg per cycle.

Limitations and safety notes

The formulas derive from very small original samples (Du Bois from 9 subjects, one of them a child), so extrapolation to the morbidly obese, cachectic, amputees, and neonates is unreliable and different formulas can diverge by 5% or more at extremes. Mosteller, Du Bois, Haycock, Gehan-George, and Boyd give slightly different results for the same patient, so a facility should standardize on one formula for reproducible chemotherapy dosing. BSA-based cytotoxic dosing poorly predicts drug clearance for most agents and is a recognized source of dose inaccuracy; it should not be treated as a pharmacokinetic surrogate.

Frequently asked questions

Which BSA formula should I use?

Mosteller is the most widely adopted for adults and children because it is simple and validates well against directly measured BSA. Du Bois remains common in cardiology and older references. For neonates and small children, Haycock or Boyd are often preferred. The key is consistency: use the same formula your institution's chemotherapy protocols were built on, since inter-formula differences can shift a calculated dose by a few percent.

Why is eGFR reported per 1.73 m²?

1.73 m² was the average BSA of a reference young adult population when GFR normalization was standardized, so kidney function is expressed as if every patient had that surface area. For drug dosing or dialysis decisions in patients whose actual BSA is far from 1.73 m² (very large or very small individuals), the eGFR should be de-indexed back to absolute mL/min using the patient's true BSA.

Should BSA be capped in obese patients for chemotherapy?

Many protocols historically capped dosing BSA at 2.0 or 2.2 m² to limit toxicity, but ASCO guidance now recommends using actual body weight to calculate full weight-based (and BSA-based) doses in obese adults for curative-intent chemotherapy, because dose-capping is associated with worse outcomes without clearly reducing toxicity. Follow the specific protocol and local pharmacy policy.

Does BSA measure body fat or nutrition?

No. BSA is a geometric estimate of skin surface area from height and weight and does not distinguish fat from lean mass. For adiposity and nutritional risk, use BMI, waist circumference, or body composition. BSA's role is purely as a size denominator for dosing and physiologic indexing.

References

  • Mosteller RD. Simplified calculation of body-surface area. N Engl J Med. 1987;317(17):1098. PMID: 3657876.
  • Du Bois D, Du Bois EF. A formula to estimate the approximate surface area if height and weight be known. 1916. Nutrition. 1989;5(5):303-11; discussion 312-3. PMID: 2520314.
  • 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):62-6. PMID: 650346.
  • Griggs JJ, Bohlke K, Balaban EP, et al. Appropriate Systemic Therapy Dosing for Obese Adult Patients With Cancer: ASCO Guideline Update. J Clin Oncol. 2021;39(18):2037-2048. PMID: 33939491.

Editorial review and citation methodology

Reviewed by the Quick Medical Calculator Editorial Team. Last reviewed: March 15, 2026. The review checks calculator inputs, intended population, interpretation, limitations, and source alignment.

  • Prefer original validation studies for scoring systems and prediction tools.
  • Use current specialty society guidance, transplant allocation policy, public health guidance, or regulator resources when they govern clinical use.
  • Include limitations and safety notes when a calculator is population-specific, context-dependent, or unsuitable as a standalone decision tool.

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