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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.

Mosteller is the starting selection for convenience. Use the formula required by the medication protocol, clinical reference, study, 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.

Formula selection

Mosteller is the calculator's starting selection for convenience, not a universal clinical default. Use the equation required by the active protocol, drug label, study, or local policy.

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.

Simple answer

How is body surface area calculated?

BSA is estimated from height and weight using a published equation. Mosteller is the calculator's starting selection for convenience, while Du Bois, Haycock, and Gehan and George can also be selected.

BSA (m²) = √[(height in cm × weight in kg) ÷ 3600]
Example: For a height of 170 cm and a weight of 70 kg: √[(170 × 70) ÷ 3600] = about 1.82 m².

Mosteller is not a universal clinical default. MedMaths also supports Du Bois, Haycock, and Gehan and George. Use the BSA formula required by the active protocol, drug label, study, or local policy. Formula-selection and comparison detail is kept in the BSA Formula Guide.

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.

Quick reference

Mosteller BSA chart by height and weight

BSA in m²

This table gives pre-calculated Mosteller BSA values for common example height and weight combinations. It is a quick arithmetic reference, not a normal-range chart and not a substitute for the patient-specific calculator or the formula required by a protocol.

Mosteller body surface area values in square metres by height in centimetres and weight in kilograms.
Height50 kg60 kg70 kg80 kg90 kg100 kg
150 cm1.441.581.711.831.942.04
160 cm1.491.631.761.8922.11
170 cm1.541.681.821.942.062.17
180 cm1.581.731.8722.122.24
190 cm1.621.781.922.052.182.3

Values are rounded to 2 decimal places for display. Use the calculator above when the exact patient measurements, another BSA equation, or a protocol-specific precision rule is required.

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. If you want to practise that next calculation step, continue to the BSA dosing lesson.

Clinical use and safety

When to use this calculator — and its limits

The arithmetic can be correct while the clinical decision is still wrong. These boundaries show what the calculator can and cannot establish.

When to use

  • Use when a protocol, medicine reference, or clinical calculation explicitly requires body surface area (BSA) in m².
  • Enter the patient’s current height and weight, then use the BSA formula named by the relevant protocol when one is specified.
  • For an order written in mg/m², BSA is an intermediate value; the prescribed mg/m² amount must still be applied to the calculated BSA.

Key limitations

  • BSA is estimated from height and weight rather than measured directly, and different published equations can return different values for the same patient.
  • Formula differences can matter more at body-size extremes. The historical Du Bois equation was derived from a very small sample, while Haycock was specifically validated across infants, children, and adults.
  • A BSA result does not establish the final medication dose. Protocol-specific BSA caps, maximum doses, organ-function adjustments, dose reductions, and rounding rules may still apply.
  • Paediatric and neonatal protocols may specify a particular BSA method; do not switch formulas simply to obtain a preferred result.

What MedMaths does not decide

  • Which BSA equation a specific protocol requires.
  • Whether a BSA cap, medication maximum dose, dose reduction, or organ-function adjustment applies.
  • Whether a medication should be prescribed or dosed by BSA for this patient.
  • The final medicine volume, preparation method, administration route, or monitoring plan.

Evidence and method checks

  • Simplified calculation of body-surface area — New England Journal of Medicine / PubMed
  • Geometric method for measuring body surface area: validated in infants, children, and adults — Journal of Pediatrics / PubMed
  • Body Surface Area Calculator — eviQ / Cancer Institute NSW
  • Body surface area in normal-weight, overweight, and obese adults — Metabolism / PubMed

Formula logic and known-value examples are checked as part of the MedMaths review process.

See how MedMaths checks calculator methods →

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)

Published BSA formulas available in this calculator

See the exact equation and original publication for each selectable formula. Formula comparison and selection guidance live in the BSA Formula Guide.

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)
Original source: Mosteller RD — Simplified calculation of body-surface area

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

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)
Original source: Haycock GB, Schwartz GJ, Wisotsky DH — Geometric method for measuring body surface area

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

Need to choose or compare BSA formulas?

This calculator performs the arithmetic for Mosteller, Du Bois, Haycock, and Gehan & George. If your question is which formula to use, why the formulas differ, or where each equation came from, use the dedicated BSA Formula Guide.

Compare BSA formulas

Important limitations of BSA

BSA is an estimate calculated from height and weight. It is useful when a protocol or clinical reference asks for body surface area, but the number should not be treated as a complete dosing decision.

BSA limitations visual explaining that different formulas can differ slightly and that a BSA result is not itself a medication dose.
  • Formula choice matters: different BSA equations can give different results from the same height and weight. Use the equation named by the relevant regimen, protocol or clinical reference.
  • Body-size extremes need context: differences between formulas may be more noticeable at unusual heights or weights. The calculator does not decide whether a dose cap or another dosing method is appropriate.
  • Paediatric use is protocol-specific: the Haycock equation was validated across premature infants, children and adults, but that does not mean every paediatric medicine should be dosed by BSA.
  • Oncology dose changes are not determined by BSA alone: current ASCO guidance supports full, weight-based cytotoxic chemotherapy dosing for obese adults with cancer rather than automatic dose reduction solely because of obesity. Treatment-specific protocols, toxicity and organ function still govern dose modification.

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.

Already have the patient's BSA and need to understand an order written in mg/m²? Read BSA medication dosing explained →

LearnBSA dosing step by step →PractiseBSA dosing quizzes →

BSA calculator and result FAQ

Direct answers about BSA results, units, supported inputs, and medication-calculation context.

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.
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.
Does this calculator choose the BSA formula for chemotherapy dosing?

Use the BSA equation specified by the active regimen, medicine label, protocol, or local policy. There is no single BSA formula that should automatically replace those instructions.

  • Mosteller is widely used and some medicine labels explicitly specify it, while other clinical resources also provide Du Bois calculations.
  • ASCO guidance on dosing in adults with obesity supports appropriate full body-size-based systemic therapy dosing; it should not be read as a universal instruction to use one particular BSA equation.
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 1.73 m² a normal BSA for medication dosing?

No. 1.73 m² is a conventional average adult BSA used to index some kidney-function results; it is not a universal normal, ideal, or target BSA for medication dosing.

  • NIDDK describes 1.73 m² as an accepted average adult BSA used for eGFR indexing.
  • Medication dosing should use the patient-specific BSA and the method required by the active protocol or drug source when BSA-based dosing is specified.
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 perform BSA arithmetic for paediatric height and weight values, but the formula and dosing method must come from the relevant paediatric protocol or medicine source.

  • The Haycock publication included premature infants, children and adults when deriving and validating its height-weight equation.
  • Some paediatric medicine labels instead specify another equation; for example, current U.S. caspofungin labelling specifies the Mosteller formula. Do not switch formulas unless the governing source allows it.

Continue calculating

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Authorship and review

Clear authorship, review timing, and limits of use.

RDFormula authorRobert D. Mosteller, MD, FACCMosteller formula · 1987Created byGeorge Lambroglou, RNFormulas, examples and safety text checked · Reviewed 16 Sep 2026
Formula researchers listed above are credited for their published work only. They are not affiliated with, reviewed by, or endorsed by MedMaths. 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.
Methodology Editorial policy Medical disclaimer Report an issue

References and formula sources

Open the original BSA formula publications and clinical context sources used for this calculator.

Original formula publications

Mosteller RD — Simplified calculation of body-surface area

PubMed

N Engl J Med. 1987;317(17):1098.

Mosteller's 1987 publication of the simplified square-root body-surface-area calculation.

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

Original article

Arch Intern Med (Chic). 1916;17(6_2):863–871.

The 1916 Du Bois and Du Bois paper describing the height-weight surface-area equation.

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

PubMed

J Pediatr. 1978;93(1):62–66.

The 1978 Haycock, Schwartz and Wisotsky study describing a formula validated across premature infants, children and adults.

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

PubMed

Cancer Chemother Rep. 1970;54(4):225–235.

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

Clinical context

DailyMed — Caspofungin acetate pediatric dosing

United States label

U.S. National Library of Medicine / DailyMed

Medicine labelling that explicitly specifies the Mosteller BSA formula, BSA × mg/m² dosing, and a medicine-specific maximum dose in pediatric patients.

ASCO — Appropriate Systemic Therapy Dosing for Obese Adult Patients With Cancer

U.S. practice guideline

J Clin Oncol. 2021;39(18):2037–2048.

Supports full body-size-based cytotoxic chemotherapy dosing in obese adults rather than automatic empirical dose reduction based on body size alone.

Fancher et al. — Comparison of BSA formulas at extremes of height and weight

Comparison study

J Oncol Pharm Pract. 2016;22(5):690–695.

Compared Mosteller and Du Bois BSA estimates across adult height and weight percentiles and examined whether formula differences could affect calculated chemotherapy doses.

NIDDK — Clinical Measurements & eGFR Accuracy

U.S. government

National Institute of Diabetes and Digestive and Kidney Diseases

Explains that 1.73 m² is an accepted average adult BSA used to normalize eGFR, not a universal target BSA for medication dosing.

eviQ — Body Surface Area Calculator

Australian oncology

Cancer Institute NSW / eviQ

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

References are provided for education, provenance and transparency. The original papers describe the equations; they do not replace a current medication protocol. For clinical dosing, follow the medication order, regimen, local policy and pharmacist or specialist guidance.

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