Body Surface Area Calculator

Introduction:

Body surface area quantifies a person's external envelope and underpins dose scaling, metabolic studies, and physiological normalisation because many biological processes correlate more closely with area than with weight. It integrates height and weight into a single metric accepted across paediatrics, oncology, nephrology, and critical-care dosing protocols. Accurate estimation matters when drug toxicity margins are narrow.

The calculator converts any common height or weight unit on-the-fly, applies five validated formulae, and reveals the mean alongside individual results, bar charts, and deviation plots. A reactive engine updates figures as you type, and a lightweight charting layer enables visual comparison without external calls, while optional CSV export supports offline reporting or electronic health-record import.

Enter 170 cm and 65 kg, select “Mosteller”, and within milliseconds you obtain a 1.75 m² estimate aligned with sibling mean values; confirm institutional rounding rules before prescribing. Use it similarly for paediatric dosing or research normalisation, but always cross-check with primary guidelines. This calculator offers informational estimates, not medical advice.

Technical Details:

Foundational Principles

BSA models treat the human body as a geometric shell where heat exchange, fluid loss, and pharmacokinetics scale more consistently with area than mass. Each empirical equation links measured height and weight to surface metrics using exponents derived from large cohort regressions, thereby bypassing expensive direct planimetry.

Formula Overview

• Mosteller: $\mathrm{BSA}=\sqrt{\frac{h\times w}{3600}}$
• Du Bois: $\mathrm{BSA}=0.20247\times h^{0.725}\times w^{0.425}$
• Haycock: $\mathrm{BSA}=0.024265\times h^{0.3964}\times w^{0.5378}$
• Gehan–George: $\mathrm{BSA}=0.0235\times h^{0.42246}\times w^{0.51456}$
• Boyd: $\mathrm{BSA}=0.0003207\times h^{0.3}\times {\mathrm{w\_g}}^{0.7285-0.0188\times \log \left(\mathrm{w\_g}\right)}$

Variables & Parameters

Scoring & Categorisation

Representative Calculation

The equation multiplies height by weight, divides by 3600, and applies a square-root. Intermediate values retain double precision to minimise rounding error.

Edge Cases & Assumptions

• Inputs below one or above three standard deviations trigger clamped predictions to avoid negative exponent artefacts.
• Boyd formula requires grams; the tool converts internally.
• All formulae assume intact limbs and normal body composition.
• Zero or blank entries suppress computation until both inputs are positive.

Performance & Stability

• Single-pass arithmetic completes under 1 ms on mainstream mobile devices.
• All computations use IEEE-754 double precision, ensuring ≈ 15 significant digits.
• The charting layer throttles redraws with a 40 ms debounce for fluid typing.

Step-by-Step Guide:

Follow this flow to generate reliable figures:

1. Enter stature in the Height field and choose centimetres, metres, or inches.
2. Enter body mass in the Weight field and set kilograms or pounds.
3. Select a preferred formula; the mean always appears for cross-checking.
4. Review the summary banner; results update automatically when any value changes.
5. Switch tabs to view a comparative table, absolute bar chart, or percentage-difference plot.
6. Download CSV only after verifying that height and weight are correct; exported rows mirror on-screen numbers exactly.

FAQ:

Glossary:

BSA

Body surface area; external body envelope.

Mosteller

Square-root formula widely used for adult dosing.

Debounce

Delay that prevents excessive redraw calls.

Percent Difference

Relative deviation from the mean value.

CSV

Comma-separated values file for spreadsheet import.