Body Surface Area Calculator

Introduction: body surface area and its clinical uses

Body surface area (BSA) estimates the total external area of a person's body. Although it is not ordinarily measured directly, BSA is widely used in healthcare because some physiological measurements are more meaningfully compared after adjustment for body size than after adjustment for weight alone. Clinicians may use BSA when reporting cardiac index, interpreting values stated per square meter, or calculating a medication regimen expressed per square meter.

BSA is particularly familiar in oncology, where a chemotherapy protocol may specify milligrams per square meter (mg/m²). A difference in calculated BSA changes the corresponding dose, so height and weight should be entered carefully and the governing protocol should be followed for dose rounding, caps, and organ-function adjustments. This calculator provides an estimate and a copyable summary; it does not make a prescribing decision.

How to use this body surface area calculator

1. Select a measurement system: Metric (cm/kg) or Imperial (in/lb).
2. Enter height and weight as positive numbers. Decimals are allowed.
3. Choose a formula: Mosteller (simple and popular) or Du Bois (older, empirically derived).
4. Optional: enter a dosage in mg/m² to estimate a total dose in mg.
5. Click Calculate to see BSA in m² and ft², plus dose if provided.
6. Click Copy Results to copy a one-line summary for notes, charts, or assignments.

For body surface area comparisons over time, such as during a treatment course, weigh under reasonably similar conditions when possible: the same scale, similar clothing, and a similar time of day can reduce variation unrelated to a meaningful change in BSA.

Body surface area formulas and unit assumptions

The BSA equations in this calculator use height in centimeters and weight in kilograms. When imperial input is selected, the calculator converts the entered height and weight before applying the chosen BSA equation:

• Inches → centimeters: multiply by 2.54
• Pounds → kilograms: multiply by 0.45359237

Body surface area is reported in square meters (m²). The calculator also presents the same BSA estimate in square feet (ft²) for reference, using 1 m² = 10.7639104167 ft².

• Mosteller (1987): BSA equals the square root of height times weight divided by 3600. $\mathrm{BSA}=\sqrt{\frac{h\times w}{3600}}$ where h is height (cm) and w is weight (kg).
• Du Bois (1916): BSA equals 0.007184 times height to the power 0.725 times weight to the power 0.425. $\mathrm{BSA}=0.007184\times h^{0.725}\times w^{0.425}$ with the same unit assumptions (cm and kg).

Worked body surface area examples

Example 1 (metric): A height of 175 cm and weight of 70 kg entered with the Mosteller equation gives: $\sqrt{\frac{175\times 70}{3600}}\approx 1.84$ The estimated BSA is therefore about 1.84 m². Expressed in square feet, the rounded value is 1.84 × 10.7639, or about 19.81 ft².

Example 2 (imperial with dosage): For a height of 68 in, weight of 150 lb, and dosage of 150 mg/m², first convert the body measurements: 68 in × 2.54 = 172.72 cm; 150 lb × 0.45359237 = 68.04 kg. The selected BSA formula gives a result of about 1.81 m². At a displayed BSA of 1.81 m², the optional dose calculation is 1.81 × 150 = 271.5 mg.

Example 3 (comparing BSA-based regimens): For the same person with a BSA of 1.60 m², a regimen of 75 mg/m² corresponds to 75 × 1.60 = 120 mg, while 100 mg/m² corresponds to 100 × 1.60 = 160 mg. The BSA estimate remains the same; changing the prescribed mg/m² rate changes the calculated total amount.

How to interpret a body surface area result

A body surface area estimate is commonly displayed to two decimal places, though the required rounding point depends on the clinical workflow. An institution may round BSA, round the final calculated dose, use dose bands, or set maximum doses. For coursework or documentation, record the BSA equation used as well as the rounding convention.

When an optional dosage is entered, this BSA calculator multiplies the rate in mg/m² by the calculated body surface area in m² to estimate a total quantity in mg. That multiplication is only one part of real-world prescribing: kidney or liver function, blood counts, toxicity, age, interactions, and the specific treatment protocol can all affect an administered dose.

Body surface area limitations, edge cases, and clinical caution

A calculated BSA is an estimate rather than a direct surface measurement. BSA equations assume broadly typical body proportions and can be less representative for children, very small or very large adults, pregnancy, edema, amputations, or unusual body composition. In obesity, a protocol may specify actual body weight, adjusted body weight, or a capped BSA according to the medication and indication.

The Du Bois equation came from a small historical sample, while the Mosteller equation is a practical simplification. Both can be useful for routine BSA estimation, but a specialized population or setting may call for another equation, such as Haycock, Gehan and George, or Boyd. This calculator intentionally compares Mosteller and Du Bois because both remain widely referenced.

For medication dosing based on body surface area, follow the applicable clinical protocol and confirm decisions with a qualified clinician. This calculator is intended for educational and informational use.

Practical notes for reliable body surface area inputs

Incorrect height, weight, or units are common causes of an incorrect BSA estimate. Before calculating, verify whether the fields are being interpreted as cm/kg or in/lb. Entering centimeters while imperial units are selected, or the reverse, can substantially distort the calculated body surface area. If a result seems implausible, check the selected units and decimal placement first.

Adult BSA estimates often fall roughly between 1.4 m² and 2.3 m², although values outside that span can occur. Children generally have lower BSAs, and very tall or heavy adults may have higher ones. Treat that range only as a prompt to recheck an entry, not as a diagnostic threshold.

Body surface area calculator FAQ

Which body surface area formula should I choose?

If no formula is specified, Mosteller is commonly chosen because it is simple and often close to other BSA methods across many body sizes. Select Du Bois when an institution, study, or assignment requires it. For clinical use, the relevant healthcare protocol takes precedence.

Why does the BSA calculator show both m² and ft²?

Square meters (m²) is the usual unit for medical BSA references and mg/m² dosing. Square feet (ft²) is included as a conversion for users who prefer an imperial area unit; it represents the same calculated surface area.

Does “Copy Results” copy the full BSA table?

The copy button copies a one-line BSA summary, such as “BSA 1.84 m² (19.81 ft²), dose 268.50 mg.” It is intended to paste cleanly into notes, spreadsheets, or messages. If clipboard permission is unavailable in your browser, the displayed text can still be selected and copied manually.

Is body surface area the same as BMI?

No. BMI (body mass index) is weight divided by height squared and is primarily a screening measure related to body-size categories. BSA estimates external body area and is used for size normalization and some dosing calculations. The two measures are not interchangeable.

Summary of this body surface area estimate

This body surface area calculator derives BSA from height and weight with either the Mosteller or Du Bois equation. It accepts metric and imperial measurements, reports BSA in m² and ft², and can multiply BSA by an optional mg/m² value to estimate mg. Use the result to check a calculation or prepare documentation, while relying on clinical guidance for treatment decisions.