Ideal Weight Formulas Compared: Devine vs Hamwi vs Robinson

Every commonly used ideal body weight formula shares the same basic structure — a base weight for 5 feet of height, plus a fixed amount per inch above that — but three different versions, developed decades apart, disagree on the exact numbers.

The shared structure

Why Devine is the most commonly used today

The Devine formula — used by this site’s calculator — has become the de facto standard largely because it’s the version most widely adopted in clinical drug-dosing calculations, where a consistent reference weight is needed for medication dosing regardless of a patient’s actual body composition. That clinical origin, not any claim of superior accuracy for general health assessment, is why it’s the most commonly cited version today.

A worked example

For a 170cm woman: convert to inches (170 ÷ 2.54 ≈ 66.9in), find inches over 5 feet (66.9 − 60 = 6.9in), then apply the formula: 45.5 + (2.3 × 6.9) ≈ 61.4kg. For a 180cm man: 50 + (2.3 × 10.9) ≈ 75.0kg.

A worked comparison across all three

For that same 170cm woman, running the height through all three formulas shows how close (and how different) they can be: Devine gives 61.4kg, Hamwi gives 45.5 + (2.2 × 6.9) ≈ 60.7kg, and Robinson gives 49 + (1.7 × 6.9) ≈ 60.7kg. All three land within about a kilogram of each other for this height — a useful illustration that for most adult heights, the specific formula chosen matters far less than whether any height-only formula is being treated as a precise personal target in the first place, which none of them were designed to be.

What none of these formulas capture

Input used	Devine / Hamwi / Robinson
Height	Yes
Gender	Yes
Frame size	No
Muscle mass / body composition	No
Age	No

All three formulas use only height and gender — none account for frame size, muscle mass, or age, despite each meaningfully affecting what a genuinely healthy weight looks like for a given individual. A muscular, athletic person will often weigh considerably more than any of these formulas suggest while carrying a healthy or even low body-fat percentage — a limitation these height-only formulas share with BMI.

A better complement: body composition and distribution

Rather than treating a single “ideal weight” number as a precise target, pairing it with a measure of fat distribution gives a fuller picture. Waist-to-hip ratio specifically measures fat distribution, which research has linked to health risk independent of total weight or BMI — a useful complement precisely because it captures something these height-only formulas structurally can’t.

How much the three formulas actually disagree

For most adult heights, Devine, Hamwi and Robinson produce results within a few kilograms of each other — they share the same basic structure and were all calibrated against similar reference populations, so wide disagreement would be surprising. The differences matter more at height extremes: because each formula uses a different per-inch coefficient, the gap between formulas widens somewhat for people well above or below average height, since a small per-inch difference compounds over more inches. For someone near average height, which formula is used matters relatively little; for someone notably tall or short, the choice can shift the result by several kilograms.

Why these formulas persist despite their limitations

It’s worth asking why height-only formulas from the 1960s-80s are still referenced today when far more precise body-composition tools exist (DEXA scans, bioelectrical impedance, skinfold calipers). The honest answer is accessibility: these formulas require no equipment beyond a height measurement, which makes them useful for quick clinical reference (particularly for drug dosing, where a consistent standardized weight matters more than an individually precise one) and for giving people a rough, immediately available reference point without needing specialized testing. They were never intended to be a precise personal health target, and treating them as one is a misapplication of what they were actually built for.

Using ideal weight formulas sensibly

Treat any of these three numbers as a rough population-based reference point — useful for clinical dosing calculations and broad screening, not as a precise personal target. Someone with an athletic build will often reasonably weigh well above the formula’s output; someone with less muscle mass may sit healthily below it. The formula’s real value is as a consistent, reproducible reference number, not a personalized health assessment.

FAQ

Which formula should I use? Devine is the most widely used today, mainly due to its clinical adoption for drug dosing — the three formulas produce broadly similar results for most heights, with differences of a few kilograms.

Why do these formulas ignore frame size? They were designed for simplicity and consistency (particularly for clinical dosing use), trading individual precision for ease of calculation — frame-size-adjusted formulas exist but are less commonly used.

Should athletes use these formulas? With caution — a muscular, athletic person will often exceed the formula’s “ideal” weight while being at a healthy or low body-fat percentage, since the formula can’t distinguish muscle mass from fat mass.

How much do the three formulas actually disagree with each other? Usually within a few kilograms for an average-height adult — the gap widens somewhat at height extremes, since each formula’s per-inch coefficient compounds differently over a larger or smaller number of inches above 5 feet.

Why do these decades-old formulas still get used when more precise tools exist? Mainly accessibility — they need only a height measurement, which makes them useful for quick clinical reference (especially standardized drug dosing) even though dedicated body-composition tools like DEXA scans are more precise for individual health assessment.