How to Calculate Your Ideal Body Weight
The question of what a person should weigh has no single perfect answer. Height, sex, age, muscle mass and body frame all play a role. That is why health professionals use several different formulas rather than one fixed table.
This guide explains the four most widely used ideal body weight formulas, shows you what each one gives for a worked example and links to the free Ideal Weight Calculator that runs all four simultaneously.
Why Ideal Weight Is a Range, Not a Single Number
Every formula for ideal weight makes different assumptions about body composition. A muscular athlete weighs more than a sedentary person of the same height, yet both may be equally healthy. This is why health guidelines express ideal weight as a range, typically spanning about 10 to 20 kilograms, and why a single target number is less meaningful than a healthy range.
The four formulas most used in clinical settings are the Devine formula, the Robinson formula, the Miller formula and the Hamwi formula. Each was developed at different times and for different original purposes, so they produce slightly different results.
The Devine Formula
Developed in 1974 by Dr B.J. Devine, this formula was originally created to calculate medication dosages for patients, not as a fitness target. It became widely adopted in medicine despite this limitation.
Devine Formula: 5 ft 6 in Woman
For men: IBW = 50 kg + 2.3 kg for each inch over 5 feet
For women: IBW = 45.5 kg + 2.3 kg for each inch over 5 feet
Example: Woman, 5 feet 6 inches (6 inches over 5 feet)
IBW = 45.5 + (2.3 × 6) = 45.5 + 13.8 = 59.3 kg (130.7 lbs)
The Robinson Formula
Developed in 1983 as a revision of the Devine formula, the Robinson formula was designed to be slightly more accurate for women and to better reflect average body compositions at the time.
Robinson Formula: Same Woman, 5 ft 6 in
For men: IBW = 52 kg + 1.9 kg for each inch over 5 feet
For women: IBW = 49 kg + 1.7 kg for each inch over 5 feet
IBW = 49 + (1.7 × 6) = 49 + 10.2 = 59.2 kg
The Miller Formula
Developed in 1983 alongside the Robinson formula, the Miller formula tends to produce the lowest ideal weight estimates of the four, which some researchers consider more appropriate for smaller-framed individuals.
Miller Formula: Same Woman, 5 ft 6 in
For men: IBW = 56.2 kg + 1.41 kg for each inch over 5 feet
For women: IBW = 53.1 kg + 1.36 kg for each inch over 5 feet
IBW = 53.1 + (1.36 × 6) = 53.1 + 8.16 = 61.26 kg
The Hamwi Formula
Developed in 1964 by G.J. Hamwi, this formula is commonly used by dietitians and nutritionists in clinical practice. It is the oldest of the four and was designed for adults of average build.
Hamwi Formula: Same Woman, 5 ft 6 in
For men: IBW = 48 kg + 2.7 kg for each inch over 5 feet
For women: IBW = 45.5 kg + 2.2 kg for each inch over 5 feet
IBW = 45.5 + (2.2 × 6) = 45.5 + 13.2 = 58.7 kg
Side by Side Comparison for a 5 Foot 6 Inch Woman
| Formula | Ideal Weight (kg) | Ideal Weight (lbs) |
|---|---|---|
| Devine (1974) | 59.3 kg | 130.7 lbs |
| Robinson (1983) | 59.2 kg | 130.5 lbs |
| Miller (1983) | 61.3 kg | 135.1 lbs |
| Hamwi (1964) | 58.7 kg | 129.4 lbs |
The four formulas give results within about 2.6 kg of each other. The healthy range for this example is approximately 58 to 62 kg. Any weight in this range is considered clinically appropriate.
Ideal Weight and BMI: How They Relate
These formulas aim to place a person within a BMI of approximately 20 to 25, which is the healthy range according to World Health Organization guidelines. Use the BMI Calculator alongside the ideal weight calculator to understand both numbers together.
BMI and ideal weight formulas were developed from population studies and do not account for individual differences in muscle mass, bone density or ethnicity. Use them as a starting point rather than a definitive target. The Body Fat Calculator gives you a more direct measure of body composition.
What These Formulas Cannot Tell You
- They do not account for muscle mass. A bodybuilder will appear above ideal weight on all four formulas despite having low body fat.
- They do not account for age-related changes in body composition. Older adults naturally have more fat and less muscle at the same weight.
- They do not apply to children. Paediatric healthy weight is assessed using growth charts.
- They were developed primarily on data from white European adults and may not apply equally across all ethnic groups.
A Practical Approach to Using These Tools
- Start with the Ideal Weight Calculator to see all four formulas at once
- Check your BMI Calculator to compare your current weight to the healthy range
- Use the Body Fat Calculator for a direct measure of body composition
- Set a calorie target using the TDEE Calculator and Calorie Calculator
- For significant weight change goals, speak with a doctor or registered dietitian for personalised guidance
Related Tools
- Ideal Weight Calculator: runs all four formulas and gives your full range
- BMI Calculator: height and weight screening
- Body Fat Calculator: direct body composition estimate
- All Health and Fitness Tools: browse all tools on CalConvs
Frequently Asked Questions
Which ideal body weight formula is most accurate?
No single formula is definitively the most accurate for all individuals. The Devine formula is the most widely used in clinical medicine. Using all four formulas together and looking at the range gives a more meaningful result than relying on any one formula alone.
Does ideal body weight change with age?
The traditional formulas do not adjust for age. In practice, health professionals allow slightly higher weights for older adults because some increase in body fat percentage is normal with ageing. Older adults may target the upper end of the healthy range rather than the midpoint.
What if I am under 5 feet tall?
These formulas were designed for adults over 5 feet tall. For shorter adults, the formulas can be applied by subtracting the per-inch adjustment for each inch below 5 feet, though this extrapolation was not part of the original research. Use the result as a rough guide only and consult a healthcare provider.
How is ideal body weight different from a healthy BMI weight?
Ideal body weight formulas and BMI-based healthy weight ranges overlap significantly but are not identical. BMI defines healthy weight as a range, while ideal weight formulas give a point estimate with an implied range. Both should be treated as general guides rather than strict targets.