Body Surface Area (BSA) Calculator

What is body surface area?

Body surface area (BSA) is the total surface area of the human body, expressed in square meters (m²). It correlates with metabolic rate, cardiac output, and drug clearance better than body weight alone for many physiological processes.

Clinicians use BSA to calculate chemotherapy doses, index cardiac output (cardiac index = CO/BSA), adjust creatinine clearance estimates, and determine burn severity (% total body surface area burned). Indexed creatinine clearance uses BSA in some nephrology formulas alongside age and sex.

Formulas estimate BSA from height and weight. Mosteller is the most widely used in modern practice because it is simple and accurate.

Du Bois BSA can underestimate surface area in morbid obesity. Mosteller tracks weight more linearly and is preferred in many hospitals today. Mosteller and Du Bois differ most at extremes of height and weight above 200 kg.

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BSA formulas compared

Mosteller (1987): BSA = √[height(cm) × weight(kg) / 3600]. Simple, accurate, and easy to compute without lookup tables. Du Bois (1916): BSA = 0.007184 × weight(kg)^0.425 × height(cm)^0.725, the classic reference used in early pharmacology research.

Haycock (1978): BSA = 0.024265 × weight(kg)^0.5378 × height(cm)^0.3964. Often preferred in pediatric dosing.

The calculator shows all three results. Values typically agree within 2 to 3% for adults of average build.

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Why multiple BSA formulas persist

Du Bois and Du Bois (1916) measured nine subjects to derive the classic power-law BSA equation used in early chemotherapy trials. Mosteller simplified the relationship in 1987 to √[height(cm) × weight(kg) / 3600], which agrees within a few percent for typical adults. Pediatric oncologists sometimes prefer Haycock or Gehan-George equations because children's proportions differ from adults.

Burn units index fluid resuscitation to BSA and age-specific charts.

Obese patients may receive capped BSA or adjusted body weight in chemotherapy protocols to avoid overdosing while still scaling to metabolic size. Protocol-specific rules override generic calculator output. Normal adult BSA near 1.73 m² is the reference for indexed cardiac output and for comparing glomerular filtration rate to population means.

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Indexed measurements using BSA

Cardiac index divides cardiac output by BSA so values near 2.5 to 4.0 L/min/m² are comparable across body sizes.

Chemotherapy regimens in mg/m² assume Mosteller or Du Bois BSA within protocol tolerances; always use the formula specified in the trial or hospital policy.

Haycock formula remains common in pediatrics because Du Bois underestimates BSA in small children.

Burn resuscitation formulas (Parkland) use weight and burn surface area, not BSA from height-weight products, so do not confuse calculators.

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BSA in everyday medicine

Contrast dye dosing and some chemotherapy agents scale to BSA. Never self-adjust infusion rates. Fitness enthusiasts rarely need BSA except when comparing indexed lab results like cardiac output in stress tests.

If weight changes more than 10% during therapy, recalculate BSA before the next oncology cycle.

Pediatric BSA below 1.0 m² should use pediatric-specific formulas when protocols require them.

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Worked BSA example and formula differences

For an adult 170 cm tall and 70 kg, Mosteller gives square root of (170 × 70 / 3600), or about 1.82 m². Du Bois gives 0.007184 × 70^0.425 × 170^0.725, also about 1.81 m². Haycock gives about 1.82 m². Agreement is close here because the example sits near the body sizes on which these equations perform similarly.

Differences grow in infants, very large adults, severe obesity, and unusual height-weight combinations.

Du Bois and Du Bois built their 1916 equation from only nine measured subjects. Haycock included infants and children. Mosteller proposed a square-root shortcut that clinicians could calculate quickly and that closely approximated older formulas in common body sizes. A protocol should name the formula it expects. Replacing Haycock with Mosteller in a pediatric oncology order or averaging formulas introduces an undocumented dosing choice. The calculator can show comparison values, but the active treatment plan controls.

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How to use the BSA calculator

Enter a current measured weight and height. Verify kilograms and centimeters after conversion, especially when copying from a chart in pounds and inches. Select the formula named by the clinical protocol. If the page displays several formulas, do not assume the mean is appropriate.

Review the result in square meters and retain at least two decimals for clinical discussion. Record formula, inputs, date, and whether weight reflects edema, ascites, pregnancy, or an amputation. Recalculate after a material weight change only when the governing protocol requires it.

Do not multiply BSA by a drug's mg/m² dose yourself. Clinicians also check maximum doses, organ function, treatment cycle, laboratory values, toxicity, and regimen-specific modifications. A numerically correct BSA can still lead to an unsafe dose when applied outside that system.

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Dosing, indexing, and limitations

BSA normalizes cardiac output and glomerular filtration to a conventional body size. A laboratory eGFR indexed to 1.73 m² may need de-indexing for selected drug-dosing decisions, but clinicians use the relevant renal equation and guidance. BSA itself is not a measure of kidney function.

The oncology team makes that decision.

ASCO guidance recommends actual body weight for cytotoxic chemotherapy dosing in many adults with obesity because arbitrary dose reduction can compromise outcomes. Individual protocols may still specify caps, organ-based reductions, or alternative dosing.

Standard equations do not directly handle amputations, severe edema, ascites, pregnancy, rapidly changing critical illness, or extreme body size. Pediatric dosing adds age, maturation, and maximum-dose safeguards. Burn surface area is a different concept measured with body maps, not height-weight BSA.

BSA is a scaling tool. A higher result does not diagnose obesity or imply worse health. Never use it to self-dose chemotherapy, contrast, cardiac medicines, or any prescription treatment.

Keep the formula name with the result when BSA enters a clinical record.

Indexing can conceal clinically relevant size at both extremes. Two people may have the same indexed cardiac output but very different absolute output, and a normalized eGFR can differ from a de-indexed value used for a specific medicine. Clinicians should state whether a result is absolute or per 1.73 m². Removing or applying the index without checking the source equation can introduce error. The calculator supplies BSA. Specialty guidance determines how, or whether, to apply it.

During cancer treatment, weight can change from tumor response, appetite loss, steroids, edema, or fluid administration. Recalculating BSA from every transient weight may not be appropriate, while ignoring sustained change may also be unsafe. Oncology protocols specify when to update weight and how to respond to toxicity. Patients should report meaningful changes and verify that the clinic has a current weight rather than trying to alter the planned dose themselves. Most equations give similar values for typical adults, but disagreement can grow at unusual heights or weights. Reproducing the same method prevents a formula change from being mistaken for a physiological change.

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Clinical applications of BSA

Oncology protocols specify chemotherapy in mg/m² based on BSA. Using actual weight without BSA adjustment in obese patients can lead to overdosing; some protocols cap BSA or use adjusted body weight. Oncology BSA caps near 2.0 m² for obese patients appear in several breast cancer protocols to limit hematologic toxicity.

Normal adult BSA ranges from approximately 1.6 m² (small adult) to 2.2 m² (large adult). Average is roughly 1.73 m², the standard used for normalizing cardiac index and glomerular filtration rate.

Never self-calculate chemotherapy or prescription doses. BSA is one input among many in clinical dosing decisions.

Amputations require adjusted height or weight inputs not handled by standard BSA formulas. Burn unit tables use Lund-Browder charts for pediatric BSA fractions; do not substitute height-weight BSA for burn surface mapping. Fitness trackers estimate calories burned using algorithms unrelated to BSA; do not mix BSA oncology math with consumer wearable outputs.

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How it works

Mosteller: BSA = √(height(cm) × weight(kg) / 3600). Du Bois and Haycock provide alternative estimates.

Frequently asked questions

• Which BSA formula is most used?Mosteller is simplest and widely used in clinical practice. Du Bois is the classic reference formula.

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References

1. Mosteller, 1987. Simplified calculation of body-surface area
2. Du Bois & Du Bois, 1916. A formula to estimate the approximate surface area
3. Haycock et al.. Geometric method for measuring body surface area
4. Pai, 2014. Chemotherapy dosing based on body surface area
5. Gurney. Body-surface area in dosing anticancer agents
6. Griggs et al.. Appropriate chemotherapy dosing for obese adult patients with cancer
7. Matzke et al.. Drug dosing considerations in patients with acute and chronic kidney disease
8. StatPearls. Lund and Browder chart for burn size estimation