The Complete Guide to Ideal Body Weight
By Arshi Khan, Founder of Just4Marketing · Last reviewed October 2026
'Ideal weight' has been estimated with several different formulas since the 1950s, each with slightly different assumptions. This guide explains where the four formulas used by this calculator came from, how they're calculated, and why you should treat the result as a range rather than a single target.
What is 'ideal weight' and why does it matter?
Ideal body weight formulas estimate a reference weight based only on height and sex. They were originally developed for clinical uses — the Devine formula, for example, was created in 1974 specifically to help standardize medication dosing calculations, not as a fitness benchmark. Over time they became popular as general weight references, even though that was never their original purpose.
Each formula follows the same basic shape: a base weight for 5 feet of height, plus a fixed amount added per inch over that, with different constants for men and women.
How the four formulas are calculated
| Formula | Base (5 ft) | Per inch over 5 ft | Origin |
|---|---|---|---|
| Hamwi (1964) | 50.0 kg men / 45.5 kg women | +2.3 kg per inch (both) | Diabetes management |
| Devine (1974) | 50.0 kg men / 45.5 kg women | +2.3 kg per inch (both) | IV medication dosing |
| Robinson (1983) | 52.0 kg men / 49.0 kg women | +1.9 kg per inch (both) | Revision of Devine |
| Miller (1983) | 56.2 kg men / 53.1 kg women | +1.41 kg per inch (both) | Revision of Devine |
This calculator uses the commonly simplified version of Hamwi that shares Devine's base weight and per-inch constant, which is why the two formulas return identical results here.
Limitations to keep in mind
Frame size isn't considered
None of these formulas adjust for whether you have a small, medium, or large bone structure, which can meaningfully shift a healthy weight up or down.
Muscle mass is ignored
A muscular athlete will often weigh well above their calculated 'ideal weight' while being lean and healthy — these formulas can't distinguish muscle from fat.
They were built for older, narrower populations
All four formulas date from 1964–1983 and were derived from specific clinical populations, not broad modern demographics.
Use the range, not a single number
Because the four formulas disagree by several pounds for most heights, the spread between them is more informative than picking one as the 'correct' answer.
Frequently asked questions
Why does the calculator show four different numbers?
Each formula — Hamwi, Devine, Robinson, and Miller — was developed independently, using different reference populations and constants. They agree closely for average heights but diverge more for very short or very tall people, which is why seeing all four gives a more honest picture than any single number.
Which formula is most accurate?
None is definitively 'most accurate' — they were originally built for different purposes (Devine, for instance, was created to standardize drug dosing calculations, not to define a fitness goal). Most sources treat the range across formulas as the useful output, not any one number.
Does ideal weight account for muscle mass or body frame?
No. These formulas only use height and sex, so they don't adjust for muscle mass, bone density, or frame size. A muscular or large-framed person will often weigh more than their 'ideal weight' figure while still being perfectly healthy.
Should I try to weigh exactly my ideal weight?
Not necessarily. These formulas are reference points from decades-old population studies, not personalized medical targets. A healthy weight range depends on your body composition, muscle mass, and overall health — best discussed with a doctor.