The short answer
The four standard formulas, Devine, Robinson, Miller and Hamwi, give different answers for the same person: at 180 cm a man gets anywhere from 71.5 kg to 77.3 kg. That spread is the honest answer. All four were built for drug dosing, not for health targets, so read the result as a range rather than a goal.
Where these formulas actually come from
This is the part almost every ideal weight calculator omits, and it changes how you should read the result.
The Devine formula was published in 1974 to calculate drug dosages, particularly for medicines where dosing by actual body weight would be dangerous in heavier patients. Robinson (1983), Miller (1983) and Hamwi (1964) followed for similar clinical purposes. None was derived from research into which weight makes people healthiest, live longest, or feel best.
They persist because they are simple and because clinicians still use them for dosing. Their migration into consumer fitness sites, where they get presented as a weight you should aim for, is a repurposing their authors never intended.
The four formulas
Each is defined as a base weight at 5 feet (152.4 cm) plus a fixed amount per additional inch:
| Formula | Men | Women |
|---|---|---|
| Devine (1974) | 50 kg + 2.3 kg per inch over 5 ft | 45.5 kg + 2.3 kg per inch |
| Robinson (1983) | 52 kg + 1.9 kg per inch | 49 kg + 1.7 kg per inch |
| Miller (1983) | 56.2 kg + 1.41 kg per inch | 53.1 kg + 1.36 kg per inch |
| Hamwi (1964) | 48 kg + 2.7 kg per inch | 45.5 kg + 2.2 kg per inch |
Worked out for a man at 180 cm, they give 75.0 kg (Devine), 72.6 kg (Robinson), 71.5 kg (Miller) and 77.3 kg (Hamwi). A spread of nearly 6 kg for the same person, from four equations that all claim to answer the same question.
Note also that the structure breaks below 5 feet: the per-inch term goes negative, which is why this calculator holds the base weight for shorter heights rather than returning a nonsensical figure.
A better reference: the WHO healthy range
Because the formulas above were never health-validated, the calculator also shows the weight range corresponding to a BMI of 18.5 to 24.9 at your height. That range comes from population health data rather than dosing convenience, which makes it the more defensible reference of the two.
For a person at 180 cm it works out to roughly 60 to 81 kg. That is a wide band, and deliberately so: healthy weight genuinely varies with build, muscle mass and individual physiology. Any calculator that hands you a single number to one decimal place is implying a precision that does not exist.
What to do with the number
Use it for orientation, not as a target:
- If your weight sits inside the WHO range and has been stable, the formulas add little. You are already where the evidence says is fine.
- If you are well above the range, the useful next questions are about trend, waist circumference and blood markers, not about closing the gap to a specific figure.
- If you are below the range, that deserves as much attention as being above it. Underweight carries real risks for bone density and immune function.
- If you train with weights, expect every one of these numbers to underestimate a healthy weight for you, because none of them can see muscle.
Getting to a weight you can actually hold
The weight you can maintain matters more than the weight you can briefly reach. Most people can hit a lower number for a few weeks through aggressive restriction; very few hold it, because the approach that produced it was never sustainable.
What works is a modest, consistent gap between what you eat and what you burn, held long enough to matter, with enough protein to keep muscle while fat comes off. The obstacle is rarely knowledge. It is that tracking what you eat, day after day, is tedious enough that people stop, and once the log has gaps it stops telling you anything.
CalAlly is built to remove that friction. Describe the meal by voice, the AI breaks it into ingredients and macros, one tap logs it, about 3 seconds. The AI coach then works from your actual data, so the feedback is about the week you really had rather than the one you meant to have.