Body Surface Area Dose Calculator
Height and weight into the Mosteller square root, then the order’s mg/m² priced against it — the way chemotherapy and pediatric dosing actually scale.
Body Surface Area Dose Calculator
Results recalculate instantly on every keystroke. Nothing you type is transmitted.
What this result does not account for
- Mosteller convention; Du Bois quoted only
- No protocol capping or rounding rules
In short: A 170 cm, 70 kg adult carries a Mosteller body surface area of 1.818119 m² — the square root of 11,900 over 3,600, and a shade above the ≈1.7 m² quoted for the average adult. At an order of 500 mg/m² the dose is 909.059343 mg. The whole point of dosing per square metre is that surface area tracks metabolic mass better than raw weight: two 80 kg patients of different heights differ in tolerance in a way weight alone cannot see.
Formula
BSA = √(height cm × weight kg ÷ 3600) ··· dose = BSA × mg/m²
Mosteller’s formula is one square root over a constant chosen so the units land on square metres — 3,600 is 60 squared, the same 60 that turns height–weight products into people-sized areas. The dose is the area times the order’s intensity. Du Bois (1916) is quoted beside it because the formulas disagree by a few percent and narrow-therapeutic-index drugs care.
Worked Example
- Enter height and weight in metric.
- Read the Mosteller surface area.
- Enter the order’s mg/m² for the dose.
- Compare the Du Bois figure before dosing a narrow-index drug.
Defaults: 170 cm, 70 kg → 1.818119 m², dose 909.059343 mg at 500 mg/m². The pediatric check: 110 cm, 18 kg → 0.741620 m². Du Bois on the default lands within 1% — quoted, not used.
Strengths & Limits Of This Model
Where this engine is strong
- One square root, shown work
- The elder formula priced beside
Where it stops
- No carboplatin AUC dosing
- No BSA-cap handling
Practical Use Cases
Chemotherapy
the mg/m² order made concrete
Pediatrics
small bodies, honest scaling
Teaching
why weight alone under-doses
Methodology & Editorial Standards
Computation runs in IEEE-754 double precision at full internal precision; rounding to two decimal places occurs strictly at the display layer, so no cumulative drift enters the result. All monetary outputs use accounting presentation — grouped thousands, two decimals, negatives in parentheses — so figures can be transcribed directly into a model or working paper. Division-by-zero and out-of-domain inputs return an em-dash rather than a misleading number.
This engine was reconciled against an independent reference implementation and hand-verified for the worked example above before release. Our full five-stage review process is published on the About Us page.
Disclaimer. This calculator is provided for informational and modelling purposes only and does not constitute financial, tax, legal, medical, or engineering advice. Verify all figures with a qualified professional before acting on them.
Body Surface Area Dose Calculator — 8 Expert FAQs
8 analyst-written answers to the questions practitioners actually ask — optimised for voice and answer-engine retrieval.
Why dose by surface area instead of weight?
Because surface area tracks cardiac output and metabolic mass more closely than weight does — two patients at the same weight but different heights carry different volumes of distribution, and the mg/m² convention absorbs that. It is a convention with a century of trial data behind it, not a law of nature: some modern protocols dose weight-based or cap the BSA used. The page computes the convention; the protocol decides.
Why 3,600 in the denominator?
It is 60 squared — a units-cancellation constant that makes height in cm times weight in kg land on square metres. Mosteller picked it for exactly that property: the formula is one square root a clinician can do on paper, which is why it outlived flashier alternatives.
Which weight should I enter?
The protocol’s weight — usually actual body weight, sometimes ideal or adjusted for obese patients, and some protocols cap BSA at 2.0 m². This page multiplies whatever body you enter; it does not second-guess the chart. Entering a weight in pounds by mistake over-doses roughly twofold, which is why the units sit in every label.
My drug order says mg/kg, not mg/m².
Then this page is not its instrument — an mg/kg order needs only the weight. Dose per square metre is the chemotherapy and pediatric convention; converting between the two conventions is a protocol decision, not arithmetic this page should guess at.
How different is Du Bois, really?
On the default body, under one percent — the reference card prints it beside the Mosteller value so the disagreement is visible. The gap grows at body extremes, and narrow-therapeutic-index drugs care about a few percent. When the two formulas disagree enough to change the dose, the protocol, not the calculator, breaks the tie.
Do fluid shifts change the surface area?
They change the weight it is built from — edema, ascites and rehydration all move the scale, and protocols specify which weight and which day the dose is computed from. The formula is honest arithmetic; entering a weight measured under different conditions is how the arithmetic inherits a lie.
Why not just use the health BSA page?
Different questions: the health page reads surface area and stops; this page carries the mg/m² order to a dose and prices the Du Bois disagreement beside it. Same square root underneath — different decisions hanging off it — which is why they remain two pages rather than one crowded one.
Do protocols really cap the BSA used?
Some do — capping at 2.0 or 2.1 square metres for obese patients is a published convention on several chemotherapy protocols, on the theory that metabolic mass does not keep rising with adipose area. This page computes the body you enter; whether to cap is written on the protocol, not in the square root.