What is the Mosteller formula for BSA?

BSA in square meters = the square root of (height in cm × weight in kg ÷ 3,600). For 170 cm and 70 kg: √(11,900 ÷ 3,600) = √3.31 ≈ 1.82 m².

How do you calculate BSA in pounds and inches?

Change the units first: divide pounds by 2.2 to get kg and multiply inches by 2.54 to get cm. Then use the Mosteller formula.

How do you calculate a dose from BSA?

Multiply the dose per square meter by the BSA. A 100 mg/m² order for a 1.82 m² patient is 100 × 1.82 = 182 mg.

Why is BSA used for some doses?

Body surface area is used to dose some medicines, such as many chemotherapy drugs, and some doses for children. Kidney function (eGFR) is also reported per 1.73 m² of body surface area.

Which BSA formula should I use on an exam?

Use the formula the question gives. Mosteller published his formula as a simpler way to find BSA: it needs only multiplication, division and a square root. Other formulas, such as Du Bois, give slightly different results.

NCLEX-RN · Free tool

Body surface area (BSA) calculator

Find body surface area in square meters with the Mosteller formula, then turn an mg/m² order into a dose. Enter metric or U.S. units; the conversions are shown.

For study only. Not for patient care or clinical decisions.

Use it to check your homework and exam practice. In practice, follow the order, your facility's policy and the product label.

Body surface area

1.82 m²

1.8181 before rounding

Multiply height by weight: 170 cm × 70 kg = 11,900.
Divide by 3,600: 11,900 ÷ 3,600 = 3.3056.
Take the square root: 1.8181 → 1.82 m².

The example (170 cm, 70 kg) is filled in. Add an mg/m² dose to see the dose in mg.

How to calculate BSA by hand

BSA (m²) = √( height in cm × weight in kg ÷ 3,600 )

Change to metric if needed: pounds ÷ 2.2 = kg, inches × 2.54 = cm.
Multiply height by weight, then divide by 3,600.
Take the square root and round to the hundredth.
For a dose, multiply the mg/m² order by the BSA.

Check your answer: a 170 cm, 70 kg adult comes out near 1.8 m². A result in the tens means a missed decimal or a skipped square root.

Frequently asked questions

What is the Mosteller formula for BSA?: BSA in square meters = the square root of (height in cm × weight in kg ÷ 3,600). For 170 cm and 70 kg: √(11,900 ÷ 3,600) = √3.31 ≈ 1.82 m².
How do you calculate BSA in pounds and inches?: Change the units first: divide pounds by 2.2 to get kg and multiply inches by 2.54 to get cm. Then use the Mosteller formula.
How do you calculate a dose from BSA?: Multiply the dose per square meter by the BSA. A 100 mg/m² order for a 1.82 m² patient is 100 × 1.82 = 182 mg.
Why is BSA used for some doses?: Body surface area is used to dose some medicines, such as many chemotherapy drugs, and some doses for children. Kidney function (eGFR) is also reported per 1.73 m² of body surface area.
Which BSA formula should I use on an exam?: Use the formula the question gives. Mosteller published his formula as a simpler way to find BSA: it needs only multiplication, division and a square root. Other formulas, such as Du Bois, give slightly different results.

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Sources

All accessed October 27, 2026.

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