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Use centimetres, metres, inches, or a feet-and-inches pair.
The primary BSA estimate always uses this measured weight.
Mosteller is the default; no single formula is universally preferred for every clinical use.
Choose a preset comparison or enter a manual reference in Advanced.
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Accepted range: 0.10–5.00 m².
m²
Use the lens that matches the source workflow.
This changes the protocol scenario table, never the primary measured-weight BSA.
Used only by optional ideal and adjusted-weight comparisons.
Accepted range: 25–45 kg/m².
kg/m²
No cap keeps the calculated formula BSA unchanged.
Accepted range: greater than 0 through 5.00 m².
m²
Zero keeps the tool in BSA-only mode.
mg/m²
Applied after any protocol cap.
Exports retain the canonical numeric values.
FormulaBSAΔ from meanReview cueCopy
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ReferenceBSADifferenceIndexCopy
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Weight basisWeightFormula BSAAfter capDoseStatusCopy
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Ideal Weight Calculator Compare four classic ideal-weight formulas by adult height, then place their spread beside a BMI corridor and optional current-weight context.
Body Metrics Calculator Compare adult BMI and waist ratios with three body-fat estimates, derived fat and lean mass plus BSA and method-spread warnings.
Growth Screening Flag Checker Screen serial child growth measurements for percentile drift and low height velocity, with age-routed adiposity checks and data-quality flags.
Projected Adult Height Calculator Estimate a child's projected adult height from current stature and parent heights, with an uncertainty range and sensitivity comparisons.

Body surface area (BSA) estimates the outside area of a body from height and weight and expresses it in square metres. It is not a direct skin measurement. The value is mainly used to scale another quantity to body size, such as a medication regimen stated in milligrams per square metre or a clinical measurement indexed to a reference BSA.

Several named equations exist because height and weight do not determine surface area exactly. Mosteller is common and simple, while Du Bois, Haycock, Gehan and George, and Boyd use different fitted exponents and constants. Their estimates are often close in ordinary adult ranges, but the spread can become more important for very small, very large, pediatric, or otherwise atypical bodies.

DecisionWhat determines itWhy it matters
FormulaThe named protocol or publicationDifferent equations can produce different BSA values.
Weight basisActual, ideal, or adjusted weight ruleChanging weight changes BSA and any derived scenario.
CapAn explicit protocol ruleA cap limits the BSA used downstream but does not change measured-weight BSA.
Dose roundingMedication and preparation policyThe final dose may move up or down to an allowed increment.

A familiar number such as 1.73 m² is often an indexing reference, not a universal normal or target. Newborn, child, and adult example lanes provide scale, but age labels alone cannot select a clinical formula or establish a safe dose.

BSA-based medication arithmetic belongs inside a current prescribing protocol and verified clinical record. Formula, height, weight, weight basis, cap, dose rate, rounding, organ function, and product constraints all need independent confirmation. This information is educational and cannot authorize treatment or replace a pharmacist or clinician.

How to Use This Tool:

Enter measured height and weight first, then select only the formula or dosing assumptions required by the relevant protocol.

  1. Enter measured Height and Weight with the correct units. Feet and inches are handled as a paired height entry.
  2. Select the Formula named by the source protocol. Mosteller is the default, not a universal clinical choice.
  3. Choose a Reference lane only for comparison, or enter a manual reference from 0.10 to 5.00 m².
  4. Use the advanced scenario controls only when a source workflow specifies a weight basis, coefficient set, BMI gate, BSA cap, dose per m², and rounding increment.
  5. Compare the five formula values and spread. Before using a dose scenario, verify which row is active and match every assumption to the current protocol and record.

Interpreting Results:

The selected BSA is the estimate from the chosen formula using measured weight. The formula range and spread show how much the five equations disagree for the same height and weight. A tight spread is ≤3% of their mean, moderate is >3% to ≤6%, and wide is >6%.

The reference index is selected BSA divided by the chosen comparison BSA, multiplied by 100. It is a relative comparison, not a percentile or statement of health.

Protocol scenarios are conditional arithmetic. Adjusted or ideal weight becomes active only when BMI is at or above the entered gate; otherwise actual weight remains active. A cap and dose rounding can then alter the scenario value. Confirm those rules independently before clinical use.

Technical Details:

Every equation receives height in centimetres and weight in kilograms, except Boyd, which uses grams in its weight term. Calculations retain full precision; the display setting controls only visible decimals.

Formula Core

The five BSA equations are evaluated side by side. H is height in centimetres, W is weight in kilograms, and Wg is weight in grams.

Mosteller=H×W3600 Du Bois=0.007184×H0.725×W0.425 Haycock=0.024265×H0.3964×W0.5378 Gehan–George=0.0235×H0.42246×W0.51456 Boyd=0.0003207×H0.3×Wg0.7285−0.0188×log10(Wg)

Formula spread in square metres is maximum minus minimum. Percentage spread divides that difference by the mean of all five estimates and multiplies by 100. Each formula's displayed delta is its value minus that mean.

Protocol Rule Core

Scenario BMI uses measured weight. Ideal body weight (IBW) applies the selected coefficient set at heights of at least 60 inches; below 60 inches, measured weight is retained. Adjusted body weight (AdjBW) moves 40% of the way from IBW toward measured weight.

IBW=b+2.3×(Hin−60) AdjBW=IBW+0.4×max(0,W−IBW)

The base b is 50 kg for the male coefficient set and 45.5 kg for the female coefficient set. Adjusted or ideal weight is selected only when measured BMI ≥ the scenario gate; the supported gate range is 25–45 kg/m².

A positive cap replaces scenario BSA with the smaller of calculated BSA and the cap. Dose equals effective BSA × dose per m², then rounds to the nearest selected 5, 10, 25, or 50 mg increment. With no increment, the unrounded dose is retained.

BSAeffective=min(BSA,cap)Dose=round(BSAeffective×rateincrement)×increment

Supported measurement domains are 20–300 cm height and 0.5–500 kg weight. Manual reference BSA accepts 0.10–5.00 m², caps accept 0–5 m², and dose rates accept 0–5,000 mg/m². Invalid values withhold the result.

Limitations and Accuracy Notes:

  • BSA equations estimate surface area from only height and weight and cannot capture every body shape.
  • Reference lanes are examples for comparison, not age-specific normal ranges or treatment recommendations.
  • Formula choice, alternative weight, BMI gate, cap, and dose rounding are protocol decisions; none is selected by physiology alone.
  • Do not use a scenario dose until height, weight, drug order, regimen, units, maximums, organ function, and preparation rules have been independently verified.

Worked Examples:

Mosteller comparison before any protocol adjustment

At 170 cm and 65 kg, Mosteller gives √(170 × 65 ÷ 3600), or about 1.75 m². The other four equations are still calculated so their range can be reviewed. A cap, alternative weight, or dose rounding changes only the optional protocol scenario, not this measured-weight estimate.

References: