BSA vs Hamwi Ideal Weight
Both calculators turn height and weight into a single body-size number, but the numbers mean very different things. The BSA calculator estimates body surface area — the approximate external surface area of the body, in square meters — using the Mosteller equation, a value used in clinical contexts where processes scale with surface area rather than weight alone. The Historical Hamwi Weight Formula Calculator produces a weight range from height using a formula from a different era, with frame multipliers that the page itself calls historical assumptions. One describes how much body you have; the other describes what a dated formula thought your weight should be.
This page compares the two calculators so you can see which model fits your purpose. It is informational, not medical advice, and neither result is a health verdict.
What each calculator does
The BSA Calculator accepts metric or imperial inputs, converts inches to centimeters and pounds to kilograms when needed, and applies the Mosteller formula: BSA equals the square root of height in centimeters times weight in kilograms divided by 3600. The result is rounded to two decimals and shown in square meters, along with the formula name and the height and weight used, so you can see whether a unit conversion happened first.
The Historical Hamwi Weight Formula Calculator takes height in centimeters or feet-and-inches, a male or female equation, and a small, medium, or large frame assumption. The base equations use height above 152.4 cm, and the frame multipliers (small 0.90–0.95, medium 0.95–1.05, large 1.05–1.10) expand the base into a range shown in kilograms or pounds. The page is explicit that the coefficients and multipliers are retained assumptions without support from the available authoritative sources.
Side-by-side comparison
| Feature | BSA Calculator | Hamwi Ideal Weight |
|---|---|---|
| Inputs | Height + weight (metric or imperial) | Height only, plus sex equation and frame assumption |
| Formula | Mosteller: √(cm × kg ÷ 3600) | 48 + 2.7 × in above 152.4 cm (male) or 45.5 + 2.2 × (female) |
| Output | Surface area in square meters | Weight range in kg or lb |
| Typical adult range | About 1.6–2.2 m² (descriptive only) | Whatever the chosen frame produces |
| Common context | Clinical body-size scaling, dosing protocols | Historical formula reproduction |
| Health verdict? | No — a scale factor, not a diagnosis | Explicitly not a health verdict |
When to use which
Use the BSA calculator when you need a body-surface-area estimate — for example, to understand how a common clinical body-size calculation is made or to follow along with a protocol that references BSA. The page emphasizes that BSA-based dosing also depends on diagnosis, kidney or liver function, lab values, age, treatment goals, and protocol-specific rules, and that you should confirm the method with the clinician, pharmacist, or written protocol involved rather than self-adjusting anything from a web result. Note that other equations exist (Du Bois, Haycock, Boyd) and may give slightly different values; this page documents the exact Mosteller calculation used here.
Use the Hamwi calculator when you want to reproduce the historical formula itself — for example, to see where a number from an older source came from. Its page is blunt about what it is not: the range is not a healthy, ideal, or recommended body weight, and it should not be compared with actual weight as a health verdict.
For body-size questions beyond these two, the BSA page points to BMI for weight relative to height and waist-to-height ratio for central body shape; the Hamwi page likewise links BMI for the separate weight-to-height screening task.
Where to start
- BSA Calculator — Mosteller body surface area estimate in square meters.
- Historical Hamwi Weight Formula Calculator — height-based historical weight range with frame multipliers.
Informational note: This page is an educational comparison, not medical advice. BSA is a body-size scale factor that must not be used to choose a medication dose on your own, and the Hamwi range is a historical formula without authoritative support. Neither number diagnoses a condition; for health questions, consult a qualified healthcare professional.