What Is an Ideal Weight Calculator?
An ideal weight calculator estimates a single target body weight based on your height and sex, using formulas originally developed by clinicians and researchers — most of them for practical purposes such as calculating safe medication dosages, not for aesthetic or fitness goals.
Unlike a healthy weight range calculator, which shows you a full band of weights considered healthy under NHS BMI guidance, an ideal weight calculator gives you one specific number per formula. Because different formulas were built with slightly different populations and assumptions in mind, they don't always agree exactly — which is why this calculator runs four of the most widely referenced formulas together and shows you an average, so you get a fuller picture rather than relying on a single equation.
The Formulas Behind This Ideal Weight Calculator
All four formulas below share the same basic structure: they start from a base weight assigned to 5 feet of height, then add a fixed amount for every inch taller than that. Here's how each one works and where it came from.
| Formula | Origin | Men (per inch over 5ft) | Women (per inch over 5ft) |
|---|---|---|---|
| Devine (1974) | Originally created for drug dosage calculations | 50kg base + 2.3kg | 45.5kg base + 2.3kg |
| Robinson (1983) | A refinement of the Devine formula | 52kg base + 1.9kg | 49kg base + 1.7kg |
| Miller (1983) | Designed to better reflect modern body composition | 56.2kg base + 1.41kg | 53.1kg base + 1.36kg |
| Hamwi (1964) | One of the earliest ideal weight formulas, still widely cited | 48kg base + 2.7kg | 45.5kg base + 2.2kg |
Because the Devine formula is the most widely used in clinical practice today, our calculator highlights it as the headline "ideal weight" figure, while showing all four individual results in the breakdown beneath your main result so you can compare them directly.
Worked example: For a woman who is 165cm (5'5") tall, the Devine formula gives 45.5kg + (2.3kg × 5 inches) = 57.0kg. The Robinson formula gives 49kg + (1.7kg × 5 inches) = 57.5kg — very close, but not identical, which illustrates why looking at more than one formula gives a more balanced estimate.
Is There an NHS Ideal Weight Calculator?
Not exactly — and it's worth being clear about this. The NHS does not publish or endorse an official "ideal body weight" formula. Instead, NHS guidance is built around BMI, using the healthy range of 18.5 to 24.9 to describe a broad, flexible band of healthy weights for a given height, rather than a single fixed number.
The ideal body weight formulas featured on this page — Devine, Robinson, Miller and Hamwi — originate from clinical and pharmacological research, where a specific numeric estimate is genuinely useful, for example when calculating drug dosages that scale with lean body mass. That's a different purpose to general health screening, which is why this calculator deliberately shows both your ideal weight estimate and your NHS healthy BMI range side by side, so you can see how the two relate.
Ideal Weight for Men vs Women
All four formulas above use different base weights and per-inch additions for men and women, reflecting average differences in frame size, muscle mass, and body composition between the sexes. Every formula starts from a lower base weight for women than for men at the same height, since women, on average, carry a lower proportion of lean muscle mass.
It's worth remembering these are population averages, not individual prescriptions — a woman with a naturally larger frame or higher muscle mass may sit well above her "ideal weight" figure while being entirely healthy, and the same applies in the other direction for men with smaller frames.
Ideal Weight vs Healthy BMI Range — What's the Difference?
These two concepts are related but not identical. Your healthy BMI range gives you a band of weights — for a given height, everything between a BMI of 18.5 and 24.9 counts as healthy. Your ideal weight, by contrast, is a single figure calculated from formulas that don't reference BMI directly at all, though the results tend to land inside or close to the healthy BMI band for most heights.
In practice, this means it's entirely normal — and not a cause for concern — if your current weight sits within your healthy BMI range but doesn't exactly match your calculated "ideal weight." The ideal weight figure is best treated as a reference point for context, not a target to chase precisely. If you'd rather see your full healthy weight range instead of a single ideal figure, try our healthy weight calculator.
Ideal body weight is an estimate, not a diagnosis or a personal goal. These formulas don't account for muscle mass, bone density, frame size, ethnicity, or age. Use your result as general context, and always speak to your GP before setting weight-related goals.
Limitations of Ideal Weight Formulas
Like BMI, ideal body weight formulas rely only on height and sex, so they cannot distinguish between muscle and fat. A muscular or athletic person will often weigh considerably more than their "ideal weight" figure while carrying very little body fat, and formulas built in the mid-20th century may not fully reflect the more diverse range of healthy body types recognised today.
These formulas were also developed using specific study populations that may not represent everyone equally across different ethnic backgrounds and body types. For a more complete picture of your health, the NHS recommends looking at your BMI, waist circumference, and overall lifestyle together, rather than focusing on a single ideal weight number.
What to Do With Your Result
If your current weight is close to your ideal weight estimate: This is a good general sign, but continue focusing on balanced nutrition and the NHS-recommended 150 minutes of moderate activity per week rather than fine-tuning to hit an exact number.
If you're noticeably below your ideal weight range: Speak to your GP, particularly if this is a recent or unexplained change, as it may be worth investigating underlying causes.
If you're noticeably above your ideal weight range: Rather than aiming for the exact "ideal" figure, focus on moving toward your NHS healthy BMI range as a more realistic and evidence-based target. The NHS Better Health campaign offers a free 12-week plan to support gradual, sustainable change.
Whatever your result shows, remember these formulas are decades-old estimation tools, not a verdict on your health or appearance. They're most useful as one data point among several — alongside BMI, waist circumference, and how you actually feel — rather than a number to obsess over.