Why "Ideal Weight" Ignores Your Build

The Devine formula takes two inputs: your height and your sex. Everything else about your body — your frame, your muscle, your age, your training history — is invisible to it. For some people that omission is trivial. For others it makes the result close to meaningless.

What gets left out

Frame size. Skeletal build varies substantially between people of the same height. A naturally broad-framed person carries more weight in bone and structural tissue than a fine-boned person of identical height, before any consideration of muscle or fat. The formula treats them identically.

Muscle mass. This is the big one. Muscle is dense, and a trained person carries considerably more of it. Someone who lifts seriously can sit well above their "ideal weight" while carrying little excess fat — the same failure mode that affects BMI, covered in BMI, muscle, and why athletes read high.

Age. Body composition shifts across a lifetime, and a weight that suits someone at 25 may not be the same weight that suits them at 65. The formula returns the same answer regardless.

Everything about health. Blood pressure, blood markers, fitness, and where fat is distributed all matter more to health outcomes than total weight — and none of them appear anywhere in the calculation.

Who the formula fits worst

You should give the result the least weight if you are:

• Muscular or actively training. Expect to read "over ideal" without that meaning anything about your body fat.
• Very tall or very short. The formula is linear — a fixed 2.3 kg per inch — which fits the middle of the height distribution better than the extremes.
• Older, with reduced muscle mass. You may sit at or under the "ideal" figure while carrying more body fat than the number implies.

What to check instead

Because "ideal weight" cannot see composition, pair it with something that can:

• Body Fat Calculator — estimates what proportion of your weight is fat rather than muscle. If your weight is above "ideal" but your body fat is unremarkable, you have your answer.
• Waist-to-Height Ratio Calculator — screens for abdominal fat, which is more strongly linked to metabolic risk than total weight. One measurement, and it captures something no height-based formula can.
• Healthy Weight Range Calculator — a better-sourced target with realistic width, as ideal weight vs healthy range explains.

Using it well anyway

None of this makes the number useless. It is a reasonable reference point, and it is genuinely useful in the clinical context it was designed for. Read it as "a typical weight for someone of this height" rather than "the weight you should be", and it does honest work.

The trouble only starts when a reference point gets treated as a goal — particularly a goal derived from a 1974 dosing formula that never claimed to be one.

The bottom line

"Ideal weight" ignores frame size, muscle, age, and every health marker, because it only knows your height and sex. If you train, are older, or sit at either extreme of height, treat it loosely and check body fat or waist-to-height ratio for a picture that includes what you are actually made of.