Body surface area calculator

What the Body Surface Area Calculator Does

This is the home of the Body Surface Area calculator, plus everything around it: a plain-English explanation of Body Surface Area, input-by-input guidance, the formula revealed, and a step-by-step worked example with real numbers. Chemotherapy doses scale to skin area, not weight — a body surface area calculator runs the Mosteller formula clinicians actually use.

You may also need our BMR calculator, Calorie calculator, Macro calculator — they cover the neighbouring calculations people usually run alongside Body Surface Area.

Quick note: this guide is for general information only and is not medical advice. If you have a health condition or a result worries you, talk to a qualified clinician.

How to Use This Calculator

Enter your figures into the fields below. Body Surface Area (BSA) estimates total skin area in square metres and is the standard scaler for chemotherapy dosing, burns assessment and some cardiac indices.

• Height: In cm or ft/in.
• Weight: In kg or lb.

The result appears instantly, with a breakdown of each step. If a figure looks unexpected, double-check your units first — metric versus imperial mix-ups are the most common cause of surprising results.

The Body Surface Area Formula

The calculator applies this standard formula:

Mosteller: BSA = √((height cm × weight kg) ÷ 3600)
Du Bois: BSA = 0.007184 × weight^0.425 × height^0.725

• Height: cm.
• Weight: kg.
• BSA: m² — typically 1.5–2.2.

Mosteller and Du Bois agree within ~3% for typical adults; Mosteller is easier to compute.

Worked Example

Here is the method applied to realistic figures:

1. Height 175 cm, weight 75 kg.
2. 175 × 75 = 13,125; ÷ 3,600 = 3.6458.
3. √3.6458 = 1.909 m².
4. A typical adult male BSA — chemotherapy would dose per m² from here.

Frequently Asked Questions

What is body surface area used for?

Mainly chemotherapy dosing, burn-size estimation, cardiac index calculation, and as the 1.73 m² reference for eGFR reporting.

What is a normal BSA?

~1.6–2.0 m² for most adults (women lower, men higher). Children scale from ~0.5 m² (infants) upward.

Mosteller vs Du Bois — which is better?

They agree closely; Mosteller’s simplicity made it the clinical favourite. Some protocols specify one — follow the protocol.

Why dose chemo by BSA instead of weight?

BSA correlates better with metabolic mass, blood volume and drug clearance than weight alone, reducing over/under-dosing across body sizes.

Can BSA estimate calories?

Roughly — basal metabolic rate scales with BSA (~35–40 kcal/m²/hour), an old physiological rule of thumb, though modern formulas beat it.

Rounding is another quiet trap. Round only the final result, never the intermediate steps — early rounding compounds through multi-step calculations and can shift the answer by more than you would expect. Let the calculator keep full precision internally and present the tidy number at the end.

Share the method, not just the answer. When Body Surface Area comes up in discussion — with a partner, an adviser, a colleague — walking through the inputs and the worked example builds agreement far faster than quoting a bare figure. People trust numbers they have seen derived; the example section above is your ready-made walkthrough.

Finally, remember that Body Surface Area is one instrument on the dashboard, not the whole dashboard. The related guides below connect it to the neighbouring calculations that complete the picture. Readers who follow those links consistently report the same thing: each individual figure makes more sense once you see how they fit together.

It is also worth stressing what Body Surface Area cannot do. No calculator captures every nuance of a real situation — unusual circumstances, edge cases and judgement calls still need a human. Use the figure as a strong, evidence-based starting point, and apply common sense (or professional advice) for the last mile. That balance is the mark of someone who uses tools well.

Bookmark this page alongside the calculator itself. Most readers return to Body Surface Area calculations at decision points — a change in income, a new goal, an annual review — and having both the tool and the explanation one click away turns each revisit into a thirty-second task instead of a research project.

A useful habit is re-running the Body Surface Area calculation whenever your circumstances change — new figures in, fresh answer out. Stale numbers are one of the quietest sources of bad decisions: the maths was right once, but the world moved on. A quick recalculation takes seconds and keeps every downstream decision honest.

If your result surprised you, treat the surprise as information rather than error. Unexpected Body Surface Area figures usually point at an input you have been estimating optimistically, a rule you did not know applied, or a genuine change worth investigating. Dig into the breakdown the calculator provides — the ‘why’ is almost always sitting in one specific line.

Consistency beats precision in tracking. Measuring Body Surface Area the same way, under the same conditions, on a regular schedule produces trends you can trust — even if any single reading carries a little noise. Pick a routine (monthly, quarterly, whatever fits) and stick to it; the pattern that emerges over time is the real insight.

When the stakes are high — a major financial decision, a medical conversation, a legal or contractual matter — pair the calculator’s output with qualified professional advice. The tool gives you speed and a solid working figure; the professional gives you judgement for your specific situation. Bring your inputs and the result to that conversation and it will be twice as productive.

One underused trick: run the calculation backwards. Start from the result you want and adjust the inputs until the calculator produces it — this ‘goal-seeking’ instantly shows what needs to change and by how much. It turns Body Surface Area from a reporting tool into a planning tool, which is where it really shines.

Keep a simple log: date, inputs, result. It sounds old-fashioned, but a running record transforms Body Surface Area from a one-off answer into a story — and stories reveal trends, plateaus and turning points that isolated numbers never show. A notes app or a single spreadsheet column is all it takes.