Ideal Weight Formulas Explained: Devine, Robinson, Miller, and Hamwi Compared

"Ideal weight" sounds like it should be a single, agreed-upon number, but in reality there are several different formulas in medical and fitness literature, each developed for a different purpose and each producing a slightly different result for the same person. Understanding where they come from helps explain why you might get several different "ideal weight" numbers depending on which calculator you use.

Why there isn't one universal formula

Most ideal weight formulas were developed decades ago for specific practical purposes — often to help clinicians estimate medication dosages — rather than as a definitive statement of what any individual should weigh. They use height and sex as inputs and produce a single number, without accounting for muscle mass, frame size, or body composition, which is why they should be read as rough reference points rather than precise targets.

The four most common formulas

Devine Formula (1974) — originally created for drug dosage calculations, this remains one of the most widely cited:

Robinson Formula (1983) — a refinement of Devine's approach with slightly adjusted constants:

Miller Formula (1983) — tends to produce slightly higher estimates than Robinson or Devine:

Hamwi Formula (1964) — one of the oldest, originally designed as a quick mental-math estimate for clinical use:

Why the results differ

All four formulas share the same basic structure — a base weight for 5 feet of height, plus an additional amount per inch above that — but the constants differ because each was calibrated against different reference populations and for different clinical goals. For a 5'10" man, the four formulas can produce ideal weight estimates that differ by 4–6 kg (roughly 9–13 lbs) from each other, which is a meaningful spread for something often treated as a single "ideal" number.

What these formulas leave out

None of these formulas account for frame size, muscle mass, or body composition — the same limitations that affect BMI. A muscular, athletic person will often weigh more than these formulas suggest without carrying excess fat, while someone with a naturally smaller frame might have a healthy weight below the formula's estimate. For that reason, these formulas are best used as one data point among several — alongside BMI, body fat percentage, and how you actually feel and function — rather than as a strict target to hit.

This calculator provides general informational estimates and is not a medical diagnosis. If you have concerns about your health or weight, consider speaking with a qualified healthcare professional.