Last updated: April 2026
Unit system
1.94 m^2
Formula: Mosteller
Body surface area is an estimate. It should not be used for medical decisions without professional guidance.
Body Surface Area estimates total external body surface area from height and weight.
The Mosteller formula is BSA = sqrt((height in cm x weight in kg) / 3600).
Different BSA formulas use different exponents and constants, so they may produce slightly different results.
BSA is an estimate and should not be used for medical decisions without professional guidance.
The Body Surface Area Calculator estimates total body surface area from height and weight. BSA is commonly used in clinical contexts and health research, but this page is only an educational calculator for understanding formulas such as Mosteller, Du Bois, and Haycock. Use this expanded guide when you need more than a quick result. It explains the assumptions behind the Body Surface Area Calculator, the records to gather, and the decisions the estimate can support. It is especially useful for users trying to understand BSA formulas shown in health calculators, medical documents, or research examples. The strongest use of the page is scenario comparison: change one input at a time, compare the output, and keep a note of which assumption changed.
The calculator converts height and weight into metric units and returns Mosteller, Du Bois, and Haycock estimates. The Mosteller formula uses the square root of height in centimetres multiplied by weight in kilograms divided by 3,600. The calculator result depends on the quality of the inputs and on the rule set or formula selected in the calculator above. For practical use, treat the output as a structured estimate: start with the core inputs, review the main outputs, then test the decision points that matter most to your situation. Key decisions include which BSA formula is being compared, whether metric conversion is correct, why two BSA estimates differ slightly.
Input: Height 180cm and weight 75kg
Calculation: sqrt((180 x 75) / 3600) = sqrt(3.75)
Result: Mosteller BSA is about 1.94 square metres.
Input: A user sees Mosteller BSA of 1.94 and Du Bois slightly different.
Calculation: The formulas apply different exponents and constants to the same height and weight.
Result: The difference is expected and should be resolved by the method specified in the relevant document.
Input: Height 70in and weight 180lb.
Calculation: The calculator converts to 177.8cm and 81.6kg before applying formulas.
Result: The user can check that unit conversion explains the final BSA.
BSA formulas were developed from different datasets and can produce slightly different answers. Seeing more than one formula helps explain why a clinical document may not match another calculator exactly.
A useful Body Surface Area Calculator result starts with the same evidence you would use if you were checking the answer manually. The calculator can organise the arithmetic, but it cannot know whether a payslip is final, a bill is estimated, a quote excludes fees, or a personal circumstance has changed since the last statement.
Before making a decision, compare the calculator result with the source document that controls the real outcome. For this topic, that usually means checking the clinical document or healthcare professional responsible for any medical use. If there is a difference between the calculator and an official statement, contract, assessment, or professional advice, treat the official document as the stronger source.
The most important input is not always the largest number on the form. Sometimes a date, threshold, percentage, eligibility flag, or timing assumption changes the result more than the headline amount. This is why scenario testing is more useful than a single calculation.
| Input | Why it matters | What to double-check |
|---|---|---|
| height | It feeds directly into the estimate or changes which rule is applied. | Check the period, units, eligibility, and whether the figure is final or estimated. |
| weight | It feeds directly into the estimate or changes which rule is applied. | Check the period, units, eligibility, and whether the figure is final or estimated. |
| unit system | It feeds directly into the estimate or changes which rule is applied. | Check the period, units, eligibility, and whether the figure is final or estimated. |
| formula choice | It feeds directly into the estimate or changes which rule is applied. | Check the period, units, eligibility, and whether the figure is final or estimated. |
| rounding precision | It feeds directly into the estimate or changes which rule is applied. | Check the period, units, eligibility, and whether the figure is final or estimated. |
The output should be read as a decision aid, not just a number. For Body Surface Area Calculator, the useful question is often what the result means for timing, affordability, eligibility, comparison, or next steps.
A single estimate is a snapshot. A better approach is to save a base case, then adjust one assumption at a time. This shows whether the result is stable or whether a small change in timing, rate, usage, income, or cost creates a very different answer.
| Scenario | Change one assumption | What the comparison shows |
|---|---|---|
| Base case | Use the best current evidence. | Shows the result you would expect if nothing important changes. |
| Conservative case | Use lower income, higher cost, slower growth, or less favourable timing. | Shows whether the decision still works with less optimistic assumptions. |
| Improved case | Use the realistic upside, such as lower cost, better rate, higher usage, or stronger evidence. | Shows the potential benefit without treating it as guaranteed. |
Most errors come from using the right formula with the wrong assumption. Dates can be counted differently, rates can change, official thresholds can move, and real bills or contracts often include conditions that a simple calculator cannot infer automatically.
Once you have a result, write down the key assumptions and compare them with the clinical document or healthcare professional responsible for any medical use. If the number affects a deadline, tax return, benefit claim, employment issue, medical question, finance agreement, or major purchase, use the calculator as preparation for a more formal check.
For lower-stakes use, the next step may simply be comparing two or three scenarios. For higher-stakes use, the next step should be checking the official guidance, speaking to the relevant organisation, or getting qualified advice before acting.
This calculator is general information only and is not medical advice. BSA may be used in clinical settings, but a healthcare professional must decide which method and measurement source is appropriate. This is general information only and is not medical advice. The calculator is designed to support understanding and planning, but it cannot verify documents, predict future rule changes, or account for every exception. Use it as an estimate and check the official source before acting where the result matters.
For general learning, compare them. For healthcare use, follow the method specified by the clinician or clinical document.
It estimates body surface area, so the output is an area measurement.
Yes. BSA formulas use weight, so a change in weight can alter the estimate.
No. It is common and simple, but Du Bois, Haycock, and other formulas also exist.
Only under professional instruction. This page does not calculate or recommend doses.
They were derived differently and weight height differently, so small differences are normal.
This calculator is designed to help you understand the likely number before you make a decision or start an application.
Your result should be checked against official UK guidance, especially if your circumstances include dependants, exemptions, prior leave, or a complex immigration history.
Treat the figure as a planning tool rather than legal advice. Where the answer affects an application deadline or major payment, speak to an authorised adviser.
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