Ideal Body Weight Formulas: Five Myths, Checked With Numbers

There is no single ideal weight for your height. The classic formulas (Devine, Robinson, Miller and Hamwi) each turn height and sex into one number, and they disagree with each other by several kilograms. They were built for practical jobs like drug dosing, not to define how anyone should look. Use them as a rough reference point next to the wider healthy BMI range, and treat every number as an estimate, not medical advice.

Below are five common beliefs about "ideal weight," each checked against real results from the Ideal Weight Calculator.

How do these formulas actually work?

All four use the same pattern: a base weight at 5 feet (60 inches), plus a fixed amount for every inch above that. Devine, for example, gives men 50 kg plus 2.3 kg per inch, and women 45.5 kg plus 2.3 kg per inch.

For a man who is 178 cm tall:

1. Convert to inches: 178 ÷ 2.54 = 70.08 in.
2. Inches over 5 ft: 70.08 − 60 = 10.08.
3. Devine: 50 + 2.3 × 10.08 = 73.18 kg.

Robinson, Miller and Hamwi swap in different base weights and per-inch amounts, so they land somewhere else.

Myth 1: "There's one correct weight for my height"

Here are all four results for the same 178 cm man:

Formula	Result
Miller	70.41 kg
Robinson	71.15 kg
Devine	73.18 kg
Hamwi	75.21 kg

That is a spread of almost 5 kg from formulas that all claim to answer the same question. The calculator reports this honestly: its headline result, Ideal weight (formula range), is a range (here 70.4–75.2 kg) rather than a single number.

Myth 2: "These formulas were designed to tell people what to weigh"

Mostly, they weren't. Devine's 1974 formula was created to estimate doses of medicines, and it is still used in clinical settings for that purpose. The others were later refinements fitted to different groups of people and different data. None was built as a personal target, and none looked at how people feel, move or stay well.

Myth 3: "Any weight above the formula number is unhealthy"

The calculator also shows the Healthy BMI range (18.5–24.9) for your height, and it's much wider. For the same 178 cm man, it's 58.6–78.9 kg, a band of about 20 kg. For a woman who is 165 cm tall, the formulas give 56.4–59.8 kg, while the healthy BMI range is 50.4–67.8 kg.

So someone a few kilograms above every formula result can still sit comfortably inside the healthy BMI band. Health also depends on things no weight number captures, like activity, sleep, blood pressure and family history. If you'd like to see where you fall, the BMI Calculator uses your actual weight.

Myth 4: "The formulas work equally well at every height"

Because each formula adds a fixed amount per inch, small differences in the per-inch amount grow with height. At 193 cm, the male results run from 78.74 kg (Miller) to 91.16 kg (Hamwi), a gap of more than 12 kg. The calculator's note warns that the formulas are least reliable for very short or very tall people. Below 5 ft, they extrapolate downward from their starting point, and the note adds that this makes them less meaningful.

The calculator accepts heights from 120 to 230 cm (47 to 90 in). Outside that range, it asks you to enter a height within it.

Myth 5: "Muscle and frame size are built in"

They aren't. The only inputs are Units, Sex and Height. Two people of the same height get identical results whether one lifts weights four times a week and the other doesn't. If body composition is what you're curious about, the Body Fat Calculator estimates it from tape measurements instead.

How to use the calculator

1. Choose Metric (cm, kg) or Imperial (in, lb) under Units, then pick Sex.
2. Enter Height. In imperial mode it's total inches: 5 ft 10 in is 70, not 5.10. Typing 5.10 is read as just over 5 inches, and you'll get the out-of-range message.
3. Read the formula range, each formula's result, and the healthy BMI range. Results update as you type and appear in the unit system you chose.

An imperial example: a man who is 70 in tall gets 155–165 lb from the formulas and 129–174 lb for the healthy BMI range. The calculation happens in your browser, and nothing you enter is saved.

FAQ

Which of the four formulas should I trust most?

None is more correct than the others for an individual. If you want one figure, the middle of the formula range is as reasonable as any single formula, but the range itself is the more honest answer.

Why are the results for women lower at the same height?

Each formula uses a separate base weight and per-inch amount for women, which reflects the data the formulas were fitted to. At 64 in, the female results run from 119.7 lb (Hamwi) to 129.1 lb (Miller).

Should I set a weight goal from these numbers?

Talk to a doctor or registered dietitian before setting a target. They can factor in your build, health and history, which no height-only formula can.

Compare all four formulas with your healthy BMI range in the Ideal Weight Calculator.