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BSA Calculator — Body Surface Area from Height and Weight

Body composition

Calculate body surface area from height and weight

Choose the required formula and enter metric or imperial measurements. Imperial values are converted to centimetres and kilograms before the published formula is applied.

Choose the formula required by the medication protocol, clinical reference, or local policy.

Choose metric or imperial inputs. The formula itself always uses cm and kg.

cm

Enter centimetres without the unit, such as 170.

kg

Enter kilograms without the unit, such as 70.

Formula units

All four published formulas use height in centimetres and weight in kilograms. Imperial entries are converted first, and those conversion steps appear in the working.

Selected formula explained

How the Mosteller formula works

Select a different method above to update this explanation. Any calculated result uses the selected formula and the same converted height and weight.

Mosteller BSA formula

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

In simple words

Multiply height in centimetres by weight in kilograms, divide by 3600, then calculate the square root.

BSA
= body surface area in square metres (m²)
height
= height in centimetres (cm)
weight
= weight in kilograms (kg)

How Mosteller differs

Mosteller uses a simplified square-root equation. It is easier to calculate manually than the exponent-based formulas, but it can return a slightly different estimate. Use the equation specified by the medication protocol, clinical reference, or local policy.

Use the formula and dosing rules named by the protocol

This calculator returns body surface area only. It does not decide whether a medicine dose should be rounded, capped, reduced, or calculated from a different weight.

BSA is a calculated estimate. For medication dosing, verify the prescribed mg/m² instruction, selected formula, body-weight input, protocol limits, and final dose independently.

What does BSA mean?

BSA means body surface area. It is an estimate of the total outside surface area of a person's body. BSA is usually expressed in square metres, written as m².

What is the definition of body surface area?

Body surface area is the estimated external area of the body. A BSA calculator uses height and weight to estimate this area because direct measurement is not practical in routine clinical care.

What does a BSA result mean?

A result of 1.82 m² means the person's estimated body surface area is 1.82 square metres. It is not the person's weight, BMI, medication dose or medicine volume.

A BSA result is not the final medication dose

If an order is written in mg/m², the prescribed amount per square metre must still be multiplied by the BSA. The relevant protocol may then require maximum-dose checks, organ-function adjustments, dose reductions, independent verification and specific rounding.

How is BSA calculated?

BSA is estimated from height and weight using a published mathematical equation. The Mosteller formula uses a square root. Du Bois and Du Bois, Haycock, and Gehan and George use different constants and mathematical powers, so the same measurements can produce slightly different results.

Mosteller BSA formula

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

In simple words

Multiply height in centimetres by weight in kilograms, divide by 3600, then calculate the square root.

BSA
= body surface area in square metres (m²)
height
= height in centimetres (cm)
weight
= weight in kilograms (kg)

All four BSA formulas explained

See each equation, what its symbols mean, how it differs and the complete arithmetic for the same height and weight.

Mosteller BSA formula

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

In simple words

Multiply height in centimetres by weight in kilograms, divide by 3600, then calculate the square root.

BSA
= body surface area in square metres (m²)
height
= height in centimetres (cm)
weight
= weight in kilograms (kg)

How this formula differs

Mosteller uses a simplified square-root equation. It is easier to calculate manually than the exponent-based formulas, but it can return a slightly different estimate.

Worked example: 170 cm and 70 kg

BSA (m²) = √[(height (cm) × weight (kg)) ÷ 3600]
BSA = √[(170 × 70) ÷ 3600]
BSA = √(11900 ÷ 3600)
BSA = √3.305556
BSA = 1.8181 m²

Result: 1.8181 m². Displayed to two decimal places: 1.82 m².

Du Bois and Du Bois BSA formula

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

In simple words

Raise height and weight to the powers shown, multiply those values together, then multiply by 0.007184.

BSA
= body surface area in square metres (m²)
height
= height in centimetres (cm)
weight
= weight in kilograms (kg)

How this formula differs

Du Bois and Du Bois is an older exponent-based equation. It applies different powers to height and weight rather than using the Mosteller square-root method.

Worked example: 170 cm and 70 kg

BSA (m²) = 0.007184 × height(cm)^0.725 × weight(kg)^0.425
BSA = 0.007184 × 170^0.725 × 70^0.425
BSA = 0.007184 × 41.4072 × 6.0837
BSA = 1.8097 m²

Result: 1.8097 m². Displayed to two decimal places: 1.81 m².

Haycock BSA formula

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

In simple words

Raise height and weight to the powers shown, multiply the results together, then multiply by 0.024265.

BSA
= body surface area in square metres (m²)
height
= height in centimetres (cm)
weight
= weight in kilograms (kg)

How this formula differs

Haycock uses coefficients derived from measurements across infants, children, and adults. It weights height and weight differently from Mosteller and Du Bois.

Worked example: 170 cm and 70 kg

BSA (m²) = 0.024265 × height(cm)^0.3964 × weight(kg)^0.5378
BSA = 0.024265 × 170^0.3964 × 70^0.5378
BSA = 0.024265 × 7.6586 × 9.8241
BSA = 1.8257 m²

Result: 1.8257 m². Displayed to two decimal places: 1.83 m².

Gehan and George BSA formula

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

In simple words

Raise height and weight to the powers shown, multiply the results together, then multiply by 0.0235.

BSA
= body surface area in square metres (m²)
height
= height in centimetres (cm)
weight
= weight in kilograms (kg)

How this formula differs

Gehan and George is another exponent-based equation. Its constants and powers differ from Du Bois and Haycock, so the same height and weight can produce a slightly different BSA.

Worked example: 170 cm and 70 kg

BSA (m²) = 0.0235 × height(cm)^0.42246 × weight(kg)^0.51456
BSA = 0.0235 × 170^0.42246 × 70^0.51456
BSA = 0.0235 × 8.7554 × 8.9005
BSA = 1.8313 m²

Result: 1.8313 m². Displayed to two decimal places: 1.83 m².

Why can BSA calculations give different results?

The equations apply height and weight differently. They use different constants, powers and source datasets. Differences can also occur when height, weight or the final result is rounded at a different stage.

Example comparison using 170 cm and 70 kg
FormulaExact estimateTwo decimals
Mosteller1.8181 m²1.82 m²
Du Bois & Du Bois1.8097 m²1.81 m²
Haycock1.8257 m²1.83 m²
Gehan & George1.8313 m²1.83 m²

Use the formula specified by the medication protocol, clinical reference or local policy. Do not change formulas merely to obtain a preferred result.

How is BSA used in medication calculations?

When a prescribed amount is written as milligrams per square metre, multiply the prescribed amount by the patient's BSA.

BSA-based medication calculation

Total amount (mg) = prescribed amount (mg/m²) × BSA (m²)

In simple words

Multiply the medicine amount prescribed for each square metre by the patient's calculated body surface area.

mg/m²
= milligrams prescribed for each square metre
BSA
= the patient's calculated body surface area in m²
mg
= the resulting total medicine amount before protocol-specific adjustments

Worked arithmetic example

Prescribed amount = 100 mg/m²
BSA = 1.82 m²
Total amount = 100 mg/m² × 1.82 m²
The m² units cancel, leaving mg
Total amount = 182 mg

This example demonstrates arithmetic only. It does not select a medicine, regimen, dose, dose cap, organ-function adjustment or final rounding method.

BSA practice questions with working

Practise each formula and a simple mg/m² multiplication example.

Mosteller metric practice: Height 170 cm and weight 70 kg. Calculate BSA using Mosteller.

Working

BSA (m²) = √[(height (cm) × weight (kg)) ÷ 3600]
BSA = √[(170 × 70) ÷ 3600]
BSA = √(11900 ÷ 3600)
BSA = √3.305556
BSA = 1.8181 m²

Displayed to two decimal places: 1.82 m²

Mosteller imperial practice: Height 5 ft 7 in and weight 154 lb. Convert the measurements and calculate BSA using Mosteller.

Working

Height = (5 × 30.48) + (7 × 2.54) = 170.18 cm
Weight = 154 × 0.45359237 = 69.85 kg
BSA (m²) = √[(height (cm) × weight (kg)) ÷ 3600]
BSA = √[(170.18 × 69.85) ÷ 3600]
BSA = √(11887.6218 ÷ 3600)
BSA = √3.302117
BSA = 1.8172 m²

Displayed to two decimal places: 1.82 m²

Formula comparison practice: Height 170 cm and weight 70 kg. Compare the displayed BSA using Mosteller and Haycock.

Working

BSA (m²) = √[(height (cm) × weight (kg)) ÷ 3600]
BSA = √[(170 × 70) ÷ 3600]
BSA = √(11900 ÷ 3600)
BSA = √3.305556
BSA = 1.8181 m²
BSA (m²) = 0.024265 × height(cm)^0.3964 × weight(kg)^0.5378
BSA = 0.024265 × 170^0.3964 × 70^0.5378
BSA = 0.024265 × 7.6586 × 9.8241
BSA = 1.8257 m²

Mosteller: 1.82 m². Haycock: 1.83 m².

Medication calculation practice: A hypothetical order is 100 mg/m² and the calculated BSA is 1.82 m². Calculate the total amount before protocol-specific rounding.

Working

Total amount (mg) = prescribed amount (mg/m²) × BSA (m²)
Total amount = 100 mg/m² × 1.82 m²
The m² units cancel, leaving mg
Total amount = 182 mg

Arithmetic result: 182 mg

BSA meaning, formulas and result FAQ

Direct answers to common body surface area searches and calculation questions.

What does BSA mean?

BSA means body surface area. It is an estimate of the total outside surface area of a person's body and is expressed in square metres (m²).

  • A BSA calculator estimates this surface area from height and weight because direct measurement is not practical in routine care.
  • BSA is different from body weight, BMI and medication dose.
What does a BSA result mean?

A BSA result such as 1.82 m² means the estimated body surface area is 1.82 square metres.

  • The number is not a medication dose by itself.
  • For an order written in mg/m², the prescribed dose per square metre must still be multiplied by the BSA.
How is BSA calculated?

BSA is estimated from height and weight using a published equation such as Mosteller, Du Bois and Du Bois, Haycock, or Gehan and George.

  • Mosteller uses a square-root equation, while the other formulas use different constants and mathematical powers.
  • Use the exact equation specified by the relevant protocol or clinical reference.
Can I calculate BSA using feet, inches and pounds?

Yes. Select imperial inputs and enter height in feet and inches and weight in pounds.

  • The calculator converts height to centimetres and weight to kilograms before applying the selected published equation.
  • The conversion steps and converted values are shown in the result working.
Which BSA formula should I use?

Use the formula specified by the medication protocol, clinical reference or local policy.

  • The calculator offers four published equations so the arithmetic can match the required method.
  • Do not switch formulas merely because another method gives a preferred number.
Why do BSA formulas give different results?

The formulas use different constants, mathematical powers and source datasets, so small differences are expected.

  • Rounding height, weight or the final BSA at different stages can also change the displayed result.
  • Use one formula consistently and follow the formula and rounding rules named by the protocol.
What does m² mean in a BSA result?

m² means square metres, the unit used to report estimated body surface area.

  • The superscript 2 means area rather than length.
  • In an mg/m² prescription, the m² in the prescribed dose cancels with the patient's BSA unit, leaving a total dose in mg.
How is BSA used in medication calculations?

For a dose written in mg/m², multiply the prescribed dose per square metre by the patient's BSA in square metres.

  • Example: 100 mg/m² × 1.82 m² = 182 mg.
  • The protocol may still require maximum-dose checks, organ-function adjustments, dose reductions and specific rounding.
How is BSA used for chemotherapy dosing?

Some chemotherapy regimens prescribe a medicine amount per square metre, written as mg/m², which is multiplied by the patient's BSA.

  • BSA is only one part of the regimen calculation.
  • Treatment protocols may also specify dose caps, organ-function changes, toxicity reductions and pharmacy verification.
Is there a normal BSA?

There is no single BSA value that should be assumed for medication dosing. BSA varies with the person's height and weight.

  • Use the patient's measured height and the weight method required by the protocol.
  • An example or standard BSA used in teaching is not a substitute for a patient-specific calculation.
Is BSA the same as BMI?

No. BMI is a weight-to-height ratio, while BSA estimates body surface area in square metres.

  • The two calculations have different equations, units and purposes.
  • They should not be substituted for one another.
Can this BSA calculator be used for children?

The calculator can show the arithmetic for the available formulas, but paediatric dosing must follow the relevant paediatric protocol.

  • The Haycock publication validated its height-weight formula across infants, children and adults.
  • That does not mean every paediatric medicine should use Haycock or BSA-based dosing.

Continue calculating

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Authorship and review

Transparent page ownership, review timing, and limits of use.

Written by

George Lambroglou, RN

Last reviewed

30 Jul 2026
This calculator estimates body surface area from height and weight. It does not select a medicine regimen, formula, dosing weight, dose cap or rounding rule.
Editorial policy Medical disclaimer Report an issue
References and formula sourcesShowHide

Original formula publications

Mosteller RD — Simplified calculation of body-surface area

PubMed

New England Journal of Medicine (1987)

Original publication of the simplified Mosteller body-surface-area calculation.

Du Bois D & Du Bois EF — A formula to estimate surface area from height and weight

Original article

Archives of Internal Medicine (1916)

Original Du Bois and Du Bois height-weight surface-area equation.

Haycock GB, Schwartz GJ, Wisotsky DH — Geometric method for measuring body surface area

PubMed

Journal of Pediatrics (1978)

Original Haycock height-weight equation validated in infants, children and adults.

Gehan EA, George SL — Estimation of human body surface area from height and weight

PubMed

Cancer Chemotherapy Reports (1970)

Original Gehan and George publication estimating body surface area from height and weight.

Clinical context

eviQ — Body Surface Area Calculator

Australian oncology

Cancer Institute NSW / eviQ

Australian clinical calculator and formula-reference page for body surface area.

StatPearls — Body Surface Area

Clinical overview

NCBI Bookshelf

Overview of BSA equations, clinical applications and limitations.

References are provided for education and transparency. For clinical dosing, follow the medication order, regimen, local protocol and pharmacist or specialist guidance.

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