Ideal Weight Calculator

Where “ideal weight” formulas came from

None of these were designed to tell you what to weigh. Devine's formula was created to calculate drug dosages, where lean mass matters and body fat does not. Hamwi's came from diabetes nutrition planning. They persist because they are simple and clinicians memorised them, not because they were ever validated as health targets.

Height is not the only input that matters

Every formula on this page takes one measurement — height — and returns a weight. That is a very small amount of information about a human being, and it explains most of the disagreement between the four results.

Things that legitimately move a healthy weight up or down, none of which these formulas can see:

• Muscle mass. Muscle is roughly 18% denser than fat. Two people the same height with the same body-fat percentage but different training histories will sit several kilograms apart, and both are fine.
• Frame size. Wrist and shoulder width vary enough to justify a ±10% adjustment, which is what the frame selector above applies.
• Age. A slightly higher BMI in later life is associated with better outcomes, partly because it provides reserve during illness.
• Ancestry. Metabolic risk begins at a lower BMI in South and East Asian populations, and at a higher one in some others.
• Pregnancy, medication and medical conditions all shift the target, sometimes substantially.

A practical way to use this page: take the healthy BMI range as your band, use the frame adjustment to place yourself inside it, and then largely ignore the number in favour of how you are actually doing — strength, energy, sleep, blood pressure and waist measurement.

Better questions than “what should I weigh?”

The reason this page shows four formulas and a range rather than one number is that the question itself is slightly wrong. Weight is a single measurement of a complicated system, and it moves for reasons that have nothing to do with health — hydration, salt, glycogen, hormones and what time you last ate all shift it by a kilogram or two within a single day.

Questions that produce more useful answers:

• Is my waist under half my height? A well-validated, thirty-second check that captures the visceral fat most associated with metabolic risk.
• Can I do the things I want to do? Carry shopping up stairs, keep up on a walk, get off the floor unaided. Function predicts quality of life far better than mass.
• Are my markers in range? Blood pressure, resting heart rate, fasting glucose and a lipid panel describe your health directly rather than by proxy.
• Is my weight stable? A steady higher weight is associated with better outcomes than repeated cycles of loss and regain.
• Am I sleeping and moving? Both improve nearly every health marker, often with no weight change at all.

If your weight sits outside the healthy band and you want to change it, aim for slow and boring: 0.5–1% of body weight per week, enough protein to keep muscle, and resistance training. Anything faster mostly costs muscle, and muscle is what you were trying to keep.

Why a range beats a number

Two people of the same height can be equally healthy twelve kilograms apart, because bone density, muscle mass, frame width and fat distribution all vary. That is why the healthy BMI band spans roughly 20 kg for an average adult — the evidence genuinely does not support a single point.

A rough frame check: wrap your thumb and middle finger around your opposite wrist. Overlapping suggests a smaller frame, just touching a medium one, and not meeting a larger one. Crude, but no worse than most alternatives, and the calculator applies a ±10% adjustment on that basis.