BSA Calculator - Three formulas compared

A BSA calculator is a body surface area calculator that turns height and weight into a single m² value used for medical dosing, burn assessment, and cardiac index calculations. The page runs the Mosteller, DuBois and DuBois, and Haycock formulas on the same height and weight so the numbers can be read side by side.

• • Chemotherapy dose preparation: multiplying a mg/m² prescription by the BSA value to get the milligram amount for a single infusion.
• • Burn percentage context: checking the rule of nines against total BSA to estimate how much skin surface is affected.
• • Cardiac index and renal dosing: producing the m² value that cardiac output and GFR-based dosing equations divide by.
• • Tracking changes across visits: comparing a current BSA to a previous one when weight or body composition has shifted between appointments.

The calculator accepts height in centimeters or inches and weight in kilograms or pounds, converts both to metric internally, and applies every formula to the same converted values. Body surface area correlates better with metabolic rate than body weight alone, which is why chemotherapy and other clinical doses are written per m² rather than per kilogram.

BSA is a clinical scaling factor that pairs naturally with the familiar BMI Calculator, which is reported alongside the BSA value here so users can see the two metrics from the same height and weight.

The calculator takes height and weight in the units selected, converts both to centimeters and kilograms, and applies the Mosteller, DuBois and DuBois, and Haycock formulas to the same metric values. The picked primary formula drives the headline BSA, and the other two are shown for comparison.

• H_cm: Height in centimeters. Inches convert to centimeters by multiplying by 2.54 before any formula runs.
• W_kg: Weight in kilograms. Pounds convert to kilograms by multiplying by 0.45359237 before any formula runs.
• Mosteller constant 3600: Empirical divisor that produces square meters when the inputs are height in centimeters and weight in kilograms.
• DuBois coefficient 0.007184: Multiplicative constant from the 1916 paper, paired with exponents 0.725 and 0.425.
• Haycock coefficient 0.024265: Multiplicative constant from the 1978 paper, paired with exponents 0.3964 and 0.5378.

All three formulas use the same two inputs and the same output unit, so the comparison row is a clean experiment in constant selection. Agreement between the three is usually within 2 to 3 percent for typical adult body sizes, with the largest spread appearing in pediatric and extreme body-size ranges.

According to Mosteller RD, N Engl J Med 1987, body surface area in square meters equals the square root of height in centimeters times weight in kilograms divided by 3600.

The Mosteller and Haycock formulas are a height-and-weight shortcut to a body-composition estimate, and the BAI Calculator offers a similar hip-and-height shortcut that produces the body adiposity index from the same kind of inputs.

The number is short, but the math behind it is not. Four ideas explain why body surface area is treated as a clinical scaling factor.

The calculator is designed so that every output traces back to the same two metric numbers, and the comparison row makes the constant-versus-exponent difference visible.

BSA is one of several body-composition estimates, and the Body Fat Percentage Calculator goes a step further by translating a few tape measurements into a body fat percentage using the US Navy method.

Two measurements, two unit selectors, and one formula picker. The steps cover the inputs, the unit conversion, and how to read the comparison row.

1. 1 Enter height and pick a unit: Type standing height in the height field, then choose centimeters or inches. The calculator converts to centimeters internally.
2. 2 Enter weight and pick a unit: Type current body weight in the weight field, then choose kilograms or pounds. The calculator converts to kilograms internally.
3. 3 Pick a primary formula: Choose Mosteller, DuBois and DuBois, or Haycock. The selected formula drives the headline BSA value.
4. 4 Read the headline BSA: The black result card shows the primary BSA in m² rounded to two decimals. This is the number to use for mg/m² dose preparation and most clinical conversations.
5. 5 Check the comparison row: The DuBois and Haycock results are listed next to the primary value, so the difference between the three formulas is visible on the same screen.
6. 6 Use the mg/m² preview as a check: Multiply the prescription rate per square meter by the primary BSA to get a milligram amount, then read the 1 mg/m² preview as a sanity check.

A nurse enters 175 cm and 78 kg, leaves the formula on Mosteller, and sees a headline BSA of 1.95 m² with DuBois 1.94 m² and Haycock 1.96 m². A chemotherapy order of 75 mg/m² becomes 1.95 times 75, or 146 mg.

When the headline BSA is interpreted alongside a treatment plan that uses lean body weight, the Lean Body Mass Calculator produces that value from the same height and weight so the two numbers can be compared on the same screen.

BSA is one of several clinical scaling factors, and the calculator is useful in specific ways that a single-formula tool or a paper table does not always cover.

• • Three formulas on the same inputs: Mosteller, DuBois, and Haycock are all applied to the same metric height and weight, so the comparison row is meaningful and the user does not have to convert anything by hand.
• • Unit flexibility for height and weight: Centimeters or inches and kilograms or pounds are accepted, with conversion to metric handled inside the calculation.
• • mg/m² dose preview: The result includes a 1 mg/m² dose preview, so a prescription rate per square meter can be multiplied against the headline BSA without an extra step.
• • Clinical range label: The calculator reports whether the result is below, inside, or above the typical 1.6 to 2.0 m² adult range.
• • Side output of BMI for context: BMI is computed from the same height and weight, so the familiar kg/m² number is available next to the m² value.
• • Works for pediatric and adult ranges: The Haycock formula is validated in infants, children, and adults, so the same calculator handles a small child and a tall adult without changing inputs.

The mg/m² preview is the practical payoff: most chemotherapy and some antibiotic orders are written per square meter, and the calculator does the multiplication in the result panel.

When a BSA result needs to be paired with a healthy-weight target for a treatment plan, the Ideal Body Weight Calculator produces a per-height ideal weight from the same metric height used here.

Two measurements feed every formula, so a few practical factors move the result more than the choice of formula.

• • All three formulas assume an average body shape for the given height and weight. People with very different proportions (limb amputation, severe scoliosis, pregnancy, or ascites) will get a BSA value that does not match their actual measured surface area.
• • The comparison row is a fairness test of the constants, not a clinical recommendation. The chosen formula should match the dosing protocol or institutional guideline, not whichever value is the most convenient.

The 1.6 to 2.0 m² adult range label is descriptive rather than a healthy range. A BSA above 2.0 m² does not mean unhealthy on its own; it means the body size is larger than average, which is what a tall person or a person with high muscle mass would show.

According to Haycock GB et al., J Pediatr 1978, the body surface area formula uses 0.024265 as the empirical coefficient and 0.3964 and 0.5378 as the height and weight exponents, and was validated against measured surface area in infants, children, and adults.

According to National Cancer Institute - Body surface area, body surface area is the standard measure used in clinical oncology for drug dosing and is a more accurate scaling factor than body weight for many chemotherapy agents

BSA is the divisor that turns a raw creatinine clearance into the indexed GFR used in kidney function reports, and the GFR Calculator applies that same indexing step to a creatinine value from a blood test.