Clinical & Hospital Pharmacy

Body Surface Area (BSA) Calculator

Estimates body surface area from height and weight with five equations, then works out a chemotherapy dose in mg and the cardiac index.

Body surface area

1.829m²

Average Adult Surface Area (1.2–2.1 m²)

Patient measurements

Height

Adults are usually 150–190 cm (59–75 in).

Weight

Actual body weight today.

BSA equation

Try an example patient

Working

The values the equation used.

Height used172cm

Weight used70kg

Body mass index (BMI)23.7kg/m²

EquationMosteller (1987)

Standard adult physiological parameters for chemotherapy and cardiac index.

1.829 m²

0.5 infant1.21.73 adult2.53.0+

Chemotherapy dose

Multiplies the prescribed mg/m² dose by this patient's BSA.

Regimen preset

Prescribed dose

mg/m²

From the regimen protocol. Typing a value switches the preset to Custom.

Cardiac output (optional)

L/min

Resting adult cardiac output is about 4–8 L/min. Leave blank to skip the cardiac index.

Individual patient dose182.9mg

Calculated as100 mg/m² × 1.83 m²

Cardiac index (normal 2.5–4.0)2.73L/min/m²

Compare all five equations

BSA rounded to 3 decimals, and the dose each would give. Tap Use to make an equation the main result.

Equation	BSA (m²)	Dose (mg)
Mosteller (1987)	1.829	182.9
DuBois & DuBois	1.825	182.5
Haycock (Pediatric)	1.834	183.4
Gehan & George	1.84	184
Boyd (1935)	1.841	184.1

1. Mosteller (1987) — standard of care

BSA (m²) = √[(height in cm × weight in kg) ÷ 3600]

2. DuBois & DuBois (1916)

BSA (m²) = 0.007184 × height(cm)^0.725 × weight(kg)^0.425

3. Haycock (1978) — children

BSA (m²) = 0.024265 × height(cm)^0.3964 × weight(kg)^0.5378

4. Gehan & George (1970) — cancer trials

BSA (m²) = 0.0235 × height(cm)^0.42246 × weight(kg)^0.51456

5. Boyd (1935)

BSA (m²) = 0.0003207 × height(cm)^0.3 × weight(g)^(0.7285 − 0.0188 × log₁₀ weight(g))

Dose and cardiac index

Dose (mg) = dose (mg/m²) × BSA · Cardiac index = cardiac output (L/min) ÷ BSA

Inches are multiplied by 2.54 and pounds by 0.453592, each rounded to one decimal, before the equations run. The individual dose uses the unrounded BSA; the comparison table uses each BSA rounded to 3 decimals, so the two can differ by 0.1 mg. BSA bands: < 1.2 m² small / paediatric, 1.2–2.1 m² average adult, > 2.1 m² large.

References: Mosteller RD, N Engl J Med 1987; ASCO guideline on appropriate chemotherapy dosing for obese adult patients with cancer, J Clin Oncol 2012 (updated 2021).

Worked example: Mosteller BSA and a dose prescribed in mg/m²

A protocol for Drug X is written as 250 mg/m². The patient in the exercise is 165 cm tall and weighs 60 kg. Calculate the body surface area with the Mosteller equation and the individual dose in mg.

Height: 165 cm
Weight: 60 kg
Equation: Mosteller
Prescribed dose: 250 mg/m²

Formula
BSA = √[(height cm × weight kg) ÷ 3600]
Substitute
BSA = √[(165 × 60) ÷ 3600] = √(9900 ÷ 3600) = √2.75
BSA
BSA = 1.6583… m² → shown as 1.658 m²
Individual dose
Dose = 250 mg/m² × 1.6583 m² = 414.58 mg → 414.6 mg
Cross-check with DuBois
0.007184 × 165^0.725 × 60^0.425 = 1.659 m² (agrees within 0.1 %)

BSA = 1.658 m²; individual dose = 414.6 mg.

The page multiplies by the unrounded BSA, so it prints 414.6 mg even though its 'Calculated as' line shows 1.66 m² (250 × 1.66 would be 415 mg), and the comparison table, which uses 1.658 m², shows 414.5 mg. Differences of this size come from rounding, not from the equation. This is an educational calculation on illustrative values: real doses follow the protocol, its rounding and capping rules, and a pharmacist's check.

Common mistakes

Putting height in metres into Mosteller. The 3600 constant assumes cm and kg; 1.65 m instead of 165 cm gives a BSA ten times too small (0.17 m²).

Using pounds or inches without converting. 132 lb is 60 kg; Mosteller with 132 gives a BSA about 48 % too high.

Forgetting the square root, which turns 1.66 m² into 2.75.

Rounding BSA to one decimal place before multiplying. 1.7 m² instead of 1.658 m² makes a 250 mg/m² dose 10 mg too large.

Switching between equations from one cycle to the next. They differ by a few per cent; using the same equation each time matters more than which one.

Using an old or stated weight. BSA should come from a current, measured height and weight.

Assumptions and limitations

Every BSA equation is an empirical fit to a small measured group (DuBois was derived from 9 people); none measures a patient's actual surface area.

The equations diverge most at the extremes — infants, very tall or very short adults, and obese or cachectic patients.

BSA-based dosing reduces, but does not remove, the variation between patients in drug clearance; organ function still has to be considered.

Some drugs have a maximum dose regardless of BSA, which this calculator does not apply.

Guide: Pharmaceutical Dose Calculations: Units, Body Weight and Body Surface AreaThe concept in full, with practice questions.BMI CalculatorBMI from the same height and weight, to see whether the patient is at a body-size extreme.Reconstitution & IV Compounding CalculatorTurn a dose in mg into a volume drawn from a reconstituted vial.IV Drip Rate CalculatorSet the rate once the dose has been made up in an infusion bag.

References

Mosteller RD. Simplified calculation of body-surface area. N Engl J Med. 1987;317(17):1098.
Stockton SJ. Stoklosa and Ansel's Pharmaceutical Calculations. 16th ed. Philadelphia: Wolters Kluwer; 2021.

Common questions

Mosteller is the simplest and the most widely used for adults, and it is what most oncology protocols assume. Haycock was validated from newborns to adults and is often preferred for children. Check your institution's policy — using the same equation every cycle matters more than which one you pick.

Not routinely. ASCO recommends full weight-based doses for obese adults, especially when treatment is curative, because capping has been linked with worse outcomes. Some individual drugs have their own caps (for example vincristine at 2 mg) — follow the protocol.

Each was fitted to a different small group of people using different measurement methods. For average-sized adults they agree within a few per cent; they diverge most for very small children and very large or very thin adults.

Cardiac index is cardiac output divided by BSA, so a large and a small patient can be compared on the same scale. About 2.5–4.0 L/min/m² is normal at rest; below 2.2 suggests low output.

Yes. Switch the unit next to each field. The calculator converts to cm and kg (rounded to 0.1) and shows the converted values in the working.

About body surface area

Body surface area (BSA), in square metres, tracks metabolic mass better than weight alone. That is why most cytotoxic chemotherapy is prescribed in mg/m² and why cardiac output is indexed to BSA. An average adult is about 1.7–1.9 m².

Use it when

Converting a chemotherapy dose in mg/m² into a dose in mg

Indexing cardiac output (cardiac index = CO ÷ BSA)

Dosing children, where Haycock is the usual equation

Comparing how much the equations differ for an unusual body size

Keep in mind

ASCO recommends full weight-based chemotherapy doses in obese adults, without arbitrary capping (for example at 2.0 m²), so curative treatment is not compromised.

For investigational or high-dose regimens, check organ function (CrCl, liver tests) and your institution's protocol before preparing a dose.

Always use a measured, current height and weight — not a stated or remembered one.

Prepared by the PharmaWallah student team. Verify results with your textbook or instructor. Report an error · Editorial policy