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MasterMath

Ideal Weight Calculator

Six formulas, six different answers: for a 175 cm man they run from about 68 to 75 kg. Seeing them side by side is the point — the disagreement tells you how soft the concept is.

Average of the formulas

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Average of the formulas—
Spread between formulas—
Devine formula—
Robinson formula—
Miller formula—
Hamwi formula—
Broca index—
Lorentz formula—
Range from a healthy BMI—

How this was worked out

    Indicative result. There is no single ideal weight. These formulas are statistical averages that ignore build, muscle mass and age.

    The formula

    Devine: 50 kg + 2.3 kg for each inch over 5 feet (men)

    Where it comes from

    Every one of these formulas started life as a clinical tool for something else. Devine was published in 1974 to calculate drug doses, not to tell anyone what to weigh. Hamwi came from diabetes management. They were adopted as weight targets long after the fact, and none of them was designed for it.

    How to work it out by hand

    1. Subtract 152.4 cm (5 feet) from your height
    2. Convert the remainder to inches by dividing by 2.54
    3. Multiply by the formula's coefficient and add its base weight
    4. Repeat with each formula and compare the spread

    What is worth knowing

    The spread between the formulas is the most honest thing here: they disagree by several kilos because each was fitted to a different population at a different time. What they all ignore is build, muscle mass and age, which is why two people of the same height can both be healthy several kilos apart. If you want a single figure to aim at, the range implied by a healthy BMI is broader and better founded — and even that is a band, not a point.

    Frequently asked questions

    Why do the formulas disagree?

    Because each was fitted to a different population for a different clinical purpose. The spread is a fair measure of how imprecise the whole idea is.

    Which formula is best?

    None of them is authoritative. Devine is the most cited because it is used for drug dosing, which is not the same as being right about body weight.

    Does this account for muscle?

    No, and that is the main weakness. They use only height and sex, so a muscular person will always come out looking heavy.

    What should I aim for instead?

    The weight range implied by a healthy BMI for your height, adjusted for how you actually feel and function. It is a band several kilos wide, not a target.