A standard BMI reading gives you a healthy range, but it treats everyone at a given height the same, regardless of whether they have a small, medium, or large bone structure. A bmi ideal weight calculation that factors in frame size gets more specific — it’s the difference between “somewhere in this 30-pound window” and a number personalized to your actual build. Here’s how frame-size-adjusted ideal weight formulas work, and how they compare to the plain BMI approach.
Why BMI Ideal Weight Alone Isn’t Always Enough
BMI ideal weight ranges are built purely from height, so they can’t account for whether someone has a naturally narrow or broad skeletal frame. Two people of identical height with different bone structures can both be at a completely healthy weight while sitting at noticeably different points within — or even outside — the standard BMI range. That gap is exactly what frame-size-based formulas were designed to address, and why a bmi ideal weight estimate benefits from an extra input beyond height alone.
The Hamwi Formula
One of the older and still widely referenced approaches to bmi ideal weight estimation is the Hamwi formula, developed for use in nutrition counseling and diabetes management:
- Men: 106 lbs for the first 5 feet of height, plus 6 lbs for every additional inch
- Women: 100 lbs for the first 5 feet of height, plus 5 lbs for every additional inch
The base number is then adjusted by frame size — roughly minus 10% for a small frame, or plus 10% for a large frame, with no adjustment for a medium frame.
The Devine Formula
The Devine formula, originally developed for medical dosing calculations, is one of the most widely used ideal body weight equations in clinical settings today:
- Men: 50 kg + 2.3 kg for each inch over 5 feet
- Women: 45.5 kg + 2.3 kg for each inch over 5 feet
Unlike Hamwi, the Devine formula doesn’t factor in frame size directly — it uses only height and sex, which makes it simpler but somewhat less personalized than a frame-adjusted bmi ideal weight approach.
How to Determine Your Frame Size
Frame size is typically estimated using wrist circumference, measured just below the wrist bone:
| Small Frame | Medium Frame | Large Frame | |
|---|---|---|---|
| Men | Under 6.5 in | 6.5–7.5 in | Over 7.5 in |
| Women | Under 5.5 in | 5.5–6.5 in | Over 6.5 in |
Once you know your frame category, it’s applied as a percentage adjustment to the base Hamwi or similar calculation, shifting the ideal weight estimate up or down from the medium-frame baseline before you arrive at a final bmi ideal weight figure.
Comparing the Approaches
Hamwi vs. Devine: Compare Your Ideal Weight
See how each formula estimates ideal weight for the same height, sex, and frame size.
Both estimates recalculate instantly as you change height, sex, or frame — nothing here is a fixed example.
| Formula | Uses Frame Size? | Basis |
|---|---|---|
| Standard BMI range | No | Height only |
| Hamwi | Yes | Height, sex, frame |
| Devine | No | Height, sex |
| Robinson | No | Height, sex |
None of these formulas is definitively “correct” — they were each developed for slightly different clinical purposes and tend to produce similar, though not identical, ideal weight estimates for the same person. Comparing two or three side by side often gives a more realistic sense of the range than trusting any single bmi ideal weight formula in isolation.
People Also Ask
What is the ideal body weight formula?
Several formulas exist — Hamwi, Devine, and Robinson are the most common — each estimating ideal weight from height and sex, with Hamwi additionally factoring in frame size.
How do I calculate my ideal weight by frame size?
Measure your wrist circumference to determine small, medium, or large frame, then apply that adjustment (roughly ±10%) to a base formula like Hamwi’s height-based calculation.
Is the Hamwi formula accurate?
It’s a reasonable estimate widely used in dietetics, but like all ideal weight formulas, it’s a population-based approximation rather than a personalized medical target.
Does frame size actually affect a healthy weight?
Yes, to a degree — bone structure contributes real weight independent of fat or muscle, so a larger-framed person can healthily weigh more than a smaller-framed person of the same height.
Get a More Personalized Estimate
Working through these formulas by hand is doable, but get a more personalized number from our ideal weight calculator, which applies this same height-and-frame logic automatically to give you a specific target range in seconds.
The Bottom Line
A bmi ideal weight estimate becomes noticeably more useful once frame size enters the picture, since it accounts for real skeletal variation that plain BMI ranges ignore. Whether you lean on the Hamwi formula, the Devine formula, or a calculator that applies them for you, the goal is the same: a more personalized target than a generic height-based range alone can offer.