Ideal Weight Formulas Explained: Devine, Robinson, and Frame Size
“Ideal weight” calculators all give slightly different numbers because they’re not one formula, they’re several, each built decades apart for a different original purpose. Here’s what’s actually behind the number, and the one adjustment most people skip.
Where these formulas actually came from
Devine, Robinson, Miller, and Hamwi were all originally developed for medical dosage calculations, not fitness goals. Doctors needed a fast way to estimate lean body weight for drug dosing before body composition scanning existed. Over time, these clinical formulas got repurposed as general “ideal weight” reference points, which is part of why they don’t perfectly match modern fitness or health targets. The broader concept of “ideal weight” itself has an even older and stranger backstory, see 6 reasons ideal weight charts don’t fit everyone.
The formulas our calculator uses
| Formula | Men | Women |
|---|---|---|
| Devine (1974) | 50 kg + 2.3 kg per inch over 5 ft | 45.5 kg + 2.3 kg per inch over 5 ft |
| Robinson | 52 kg + 1.9 kg per inch over 5 ft | 49 kg + 1.7 kg per inch over 5 ft |
Run your height through both instantly with our ideal weight calculator.
The adjustment most calculators skip: body frame size
A person with a naturally larger skeletal frame will weigh more at the same height without carrying more fat, and the standard formulas don’t account for this on their own. Frame size is typically estimated using wrist circumference relative to height, and the common adjustment is straightforward:
- Small frame: subtract about 10% from the formula result
- Medium frame: use the formula result as-is
- Large frame: add about 10% to the formula result
This single adjustment is why two people of identical height can have genuinely different healthy weights, and why a single unadjusted number shouldn’t be treated as a strict target.
Worked example
A 5’10” (70 inch) man, 10 inches over the 5-foot baseline:
| Formula | Base calculation | Result |
|---|---|---|
| Devine | 50 + (2.3 × 10) | 73 kg (~161 lb) |
| Robinson | 52 + (1.9 × 10) | 71 kg (~157 lb) |
With a large frame adjustment (+10%), the Devine estimate shifts to roughly 80 kg (~176 lb), a meaningfully different number from the unadjusted 73 kg.
Why the formulas disagree with each other
Each formula was built from a different reference population at a different time, so a 5-10 pound spread between formulas for the same height is normal, not an error. That’s exactly why showing more than one formula side by side is more honest than presenting a single number as definitive.
What these formulas don’t account for
- Muscle mass, an athlete’s healthy weight is routinely above formula estimates
- Age-related changes in muscle and bone density
- Personal health goals beyond a population-average reference point
Why do ideal weight calculators give different results?
Because they use different formulas (Devine, Robinson, Miller, or Hamwi), each developed from a different reference population at a different time. Small differences between them are expected, not an error.
How do I know my body frame size?
Frame size is commonly estimated from wrist circumference relative to height. A smaller wrist relative to height generally indicates a small frame, while a larger one indicates a large frame; medium frame covers most people.
Should I use my exact ideal weight formula result as a target?
No. Treat it as a general reference range, especially once adjusted for frame size, rather than a strict number to hit, since muscle mass and individual body composition affect what’s genuinely healthy for you.
Written by EquateWorld Team
Part of the EquateWorld editorial team.
