Ideal Weight Calculator

Ideal body weight is a reference figure — a single estimate of what a person's weight would be, based purely on height and sex, without factoring in their actual current weight, muscle mass, or frame size. It's a starting point for comparison, not a target to force yourself toward.

This calculator uses the Devine formula, originally developed in 1974 to help clinicians estimate a patient's weight for calculating accurate drug dosages (like the antibiotic gentamicin, where dosing by actual body weight can be misleading in people who carry a lot of extra fat or fluid). It has since become the most widely referenced reference-weight formula in clinical practice — more commonly cited than alternatives like the Robinson, Miller, or Hamwi formulas. It sets a base weight at 5 feet tall (50 kg for men, 45.5 kg for women) and adds 2.3 kg for every inch above that.

Because the formula only uses height and sex, it doesn't know anything about your actual body composition — a muscular, athletic person will often weigh noticeably more than their "ideal weight" here while being perfectly healthy. For a fuller picture, use this alongside BMI or Body Fat Calculator rather than treating this number in isolation.

A worked example

Take a man who is 170 cm tall. Convert to inches: 170 ÷ 2.54 ≈ 66.93 in. The Devine formula starts at 50 kg for 5 feet (60 inches) and adds 2.3 kg per inch above that: 50 + 2.3 × (66.93 − 60) = 50 + 2.3 × 6.93 ≈ 65.9 kg. For a woman at the same height, the base is 45.5 kg instead of 50: 45.5 + 2.3 × 6.93 ≈ 61.4 kg — a 4.5 kg difference from the male result, entirely from the formula's starting constant.

A common misconception

The word "ideal" makes this sound like a target to hit, but the formula was never built for that purpose — it was created in 1974 specifically to help clinicians estimate drug dosages, like the antibiotic gentamicin, in situations where dosing by actual body weight could be misleading. Being above or below your "ideal weight" here says nothing on its own about your health; it's a population-level reference figure, not a personal goal.

What the formula doesn't account for

Devine's formula only ever needs two inputs — height and sex — which means it has no way to know anything about your build. An earlier formula, developed by G.J. Hamwi in 1964 and one of Devine's own starting points a decade later, addressed this partially by letting clinicians adjust the result up or down by about 10% for a small or large body frame — an adjustment Devine's version dropped entirely. Because of that, a naturally large-framed or heavily muscled person will often weigh well above this number while being perfectly healthy, and a small-framed person may sit comfortably below it.

How to use this number

Use it as one reference point among several, not a number to chase. It's most useful as a rough sanity check — is your actual weight in the same general neighborhood as this estimate, or meaningfully different in a way worth understanding — rather than as a precise target. If your weight sits well outside this figure, body composition tools like Body Fat Calculator or BMI Calculator, alongside a conversation with a doctor, will tell you far more than this number alone.

Ideal weight vs. BMI's healthy range

BMI Calculator gives you a healthy weight range for your height — an entire band, since BMI's 18.5–24.9 "normal" category spans a wide range of individual weights. Ideal Weight Calculator instead gives a single reference figure with no range at all. The two will usually overlap loosely, but they're built differently — BMI's range comes from population health-outcome data, while the Devine formula's single figure comes from a clinical dosing convention — so don't be surprised if they don't point to exactly the same number.