CalcKit"What should I weigh?" is one of the most-searched health questions, and the honest answer is that there is no single ideal weight for any height. Your healthy weight is a range, not a target on the scale, and where you sit inside that range depends on muscle, frame, age and body composition. Two methods are used to work it out: the healthy BMI range, which is the better guide for setting a personal goal, and the Devine formula, a classic clinical rule that gives one reference number from your height and sex. Here is how to calculate both.
Method 1: the healthy BMI range
The World Health Organization defines a healthy adult BMI as 18.5 to 24.9. Because BMI is weight divided by height squared, you can turn that range back into a weight range for your height with a simple formula:
Low end = 18.5 × height in metres² · High end = 24.9 × height in metres²
Take a man who is 175 cm tall (1.75 m). His height squared is 1.75 × 1.75 = 3.0625. Multiply by 18.5 for the low end: 18.5 × 3.0625 = 56.7 kg. Multiply by 24.9 for the high end: 24.9 × 3.0625 = 76.3 kg. So his healthy weight range is roughly 56.7 to 76.3 kg — a span of nearly 20 kg, which is the point: the range is the answer, not one number inside it. Try your own height in our free BMI Calculator — it shows your healthy weight range instantly.
Method 2: the Devine formula
The Devine formula is the best-known "ideal body weight" equation. It was published in 1974 by pharmacist B. J. Devine as a rule for estimating drug doses, not as a health target — but it is still the reference figure most clinicians quote:
Men: 50 kg + 2.3 kg for every inch over 5 feet
Women: 45.5 kg + 2.3 kg for every inch over 5 feet
Take a woman who is 165 cm tall (5 ft 5 in). She is 5 inches over 5 feet, so her Devine weight is 45.5 + (2.3 × 5) = 57 kg. Her healthy BMI range, by contrast, is 50.4 to 67.8 kg — the Devine figure sits comfortably inside it, as it usually does near average height. For a taller man, say 180 cm (5 ft 11 in), Devine gives 50 + (2.3 × 11) = 75 kg, inside a BMI range of 59.9 to 80.7 kg. The two methods agree well around average heights and drift apart at the extremes, which is why the formulas were only ever validated for adults roughly between 5 ft and 6 ft 4 in.
Which method should you use?
For a personal weight goal, use the BMI range. It is built from population health data, it gives you room to aim for the middle rather than a single number, and it is the same standard your doctor uses. The Devine formula is better treated as a reference point — a single figure to compare against, useful when a clinician needs one standardised weight for dosing or nutrition planning. If the two disagree by a lot, trust the range, not the single number. And remember that neither method knows anything about your build: the same height can carry very different healthy weights depending on how much of it is muscle.
What the formulas can't see
Height-only formulas ignore the things that matter most about your body. A muscular person can sit above their "ideal" weight with very little body fat, while someone inside the range can still carry too much fat around the waist. Frame size, age, sex and ethnicity all shift what a healthy weight looks like, and no equation captures them. That is why BMI is called a screening tool, not a diagnosis. Pair your weight range with a second check — our free Body Fat Calculator estimates body fat from tape measurements, and waist size is often a better warning sign than the scale alone.
How to use your result
First, calculate your healthy weight range and see where your current weight falls. If you are inside it, your goal is maintenance, not chasing a lower number. If you are outside it, pick a first target at the nearest edge of the range rather than the middle — a 5–10% change is a realistic first step, and slow change stays off. Then work out the daily calories that support that target with our free Calorie Calculator, and re-check your range every few months rather than every day. If you are pregnant, under 18, over 60, or managing a medical condition, treat these figures as a starting point for a conversation with a clinician, not a goal you set alone.