Ideal Weight Calculator

How to use the ideal weight calculator

This tool runs four published ideal body weight equations against one height and prints what each of them calculates. Choose the male or female coefficient set, enter a height in centimetres or inches, and the page returns four numbers in kilograms and pounds along with the band they span. The default is a 175 cm male body.

Nothing else is asked of you because nothing else was ever asked of these formulas: height and sex are the entire input, which is the first and largest thing to understand about the output. What comes back is an estimate produced by a named equation, not a statement about the person who typed the height in.

It is worth knowing what each formula was actually built for, because none of the four was designed as a health target. The Devine equation was published by B. J. Devine in Drug Intelligence and Clinical Pharmacy in 1974 in the course of work on gentamicin antibiotic dosing, and it survives today mostly because clinical pharmacy adopted it for scaling drug doses to body size.

Robinson and colleagues published their revision in the American Journal of Hospital Pharmacy in 1983, and Miller and colleagues published theirs in the same journal the same year, both aimed at drug dosage calculation. The Hamwi figures come from a chapter by G. J. Hamwi in the American Diabetes Association volume Diabetes Mellitus: Diagnosis and Treatment in 1964, written for dietetics practice. Dosing heuristics and dietetics shorthand, in other words, not weight goals.

What this page will not do is tell anyone what to weigh. It reports the arithmetic four dated equations perform on a height, and that is categorically different from a health assessment. The formulas cannot see muscle mass, frame size, bone density, body composition, age, ethnicity, pregnancy, medication or any medical history, because none of that was ever an input.

A person carrying substantial muscle can sit far above every one of these estimates in excellent health, and a small-framed person can sit below them in equally good health. Below roughly 152.4 cm, which is the 5 foot baseline the equations start from, the formulas have no defined slope at all and the tool simply holds them at their base value.

Where the four formulas drift apart

Read the four numbers as a band and pay attention to how wide it is. At 175 cm the male band runs 68.7 to 72.0 kg, a spread of 3.3 kg, because that is close to the average height the equations were fitted around and they happen to agree there.

Move away from the middle and they come apart fast. At 200 cm the same four equations estimate anywhere from 82.6 kg to 98.6 kg, a disagreement of 16 kg, because Hamwi adds 2.7 kg per inch while Miller adds only 1.41 kg per inch, and that slope difference compounds with every inch.

The reference table above shows the band and the spread at twelve heights so the pattern is visible in one glance. Four respected equations that differ by 16 kg on the same body cannot all be describing one correct answer.

The formula, worked line by line

All four equations share one shape. Each starts from a base weight in kilograms for a body exactly 5 feet, or 60 inches, tall, then adds a fixed increment for every inch above that. A height in centimetres is divided by 2.54 to get inches, 60 is subtracted, and the remainder drives everything.

What separates the four is only which base and which increment they chose: Hamwi is the steepest at 2.7 kg per inch for male bodies, Miller the flattest at 1.41 kg per inch.

Those choices were made independently and for different jobs. Devine 1974 came out of gentamicin dosing work in Drug Intelligence and Clinical Pharmacy. Robinson 1983 and Miller 1983 were both published in the American Journal of Hospital Pharmacy as revisions aimed at drug dosage calculation. Hamwi 1964 was a dietetics shorthand from an American Diabetes Association volume.

None of them was derived as a health target, none has been shown to supersede the others, and this tool therefore reports all four rather than choosing a winner.

estimate kg = base + increment x (height in inches − 60)
male   base / increment: Devine 50 / 2.3, Robinson 52 / 1.9, Miller 56.2 / 1.41, Hamwi 48 / 2.7
female base / increment: Devine 45.5 / 2.3, Robinson 49 / 1.7, Miller 53.1 / 1.36, Hamwi 45.5 / 2.2
175 cm = 68.9 in = 8.9 in over 5 ft  ->  68.7 to 72.0 kg across the four

The spread is the number worth carrying away, and it is not constant. Because Hamwi adds 2.7 kg per inch and Miller adds 1.41 kg per inch, the two lines cross at about 6.36 inches over the baseline, roughly 168.5 cm, which is why the male estimates bunch to within 1.5 kg near 170 cm and then fan out on both sides.

At 205 cm the same four equations estimate 85.4 kg and 103.9 kg at the extremes, 18.5 kg apart, which is more than the entire difference the average person would ever discuss with a clinician.

None of this is medical advice, a diagnosis or a target. These are dated heuristics built for drug dosing and dietetics shorthand between 1964 and 1983, and they were never validated as statements about what is healthy for an individual. They cannot account for muscle mass, frame size, body composition, age, ethnicity, pregnancy, medication or medical history, because a height and a sex flag are the only things they were ever given.

A muscular or large-framed person can be in excellent health well above every number on this page, and a small-framed person well below it. If a figure here prompts a question about your own weight or health, the useful next step is a conversation with a doctor or a registered dietitian who can weigh the things these equations cannot see.

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