Ideal body weight formulas produce a single target number from your height and sex. They are used in clinical settings for drug dosing and ventilator settings, and they have leaked into general use as a personal goal weight.
There is something worth knowing before you use one. Despite what most articles imply, the established ideal weight formulas do not include age as a variable. They were derived for clinical purposes from height and sex alone. Age genuinely does affect healthy body composition – but not through these equations.
This guide covers the four main formulas, works through examples, compares them against BMI-derived ranges, and explains what age actually changes.
Key Takeaways
- The four standard formulas – Devine, Robinson, Miller and Hamwi – all use height and sex only.
- For the same person they can disagree by 5 kg or more, which tells you something about their precision.
- A BMI-derived healthy range is wider and generally more useful than a single target number.
- Age affects body composition and muscle mass, but is not an input to these formulas.
- None of them account for frame size, muscle mass, or body composition.
The Four Standard Formulas
All four share the same structure: a base weight for a person of 5 feet (152 cm), plus a fixed increment for each additional inch. They differ only in the base and the increment, which is why they disagree.
All are expressed in kilograms, with height in inches above 5 feet.
Devine is the most commonly used, largely because it became the standard for clinical drug dosing rather than because it is the most accurate for defining a healthy weight. That distinction matters: these were built for medical calculations, not as personal targets.
| Formula | Men | Women |
|---|---|---|
| Devine (1974) | 50 kg + 2.3 kg per inch over 5 ft | 45.5 kg + 2.3 kg per inch |
| Robinson (1983) | 52 kg + 1.9 kg per inch | 49 kg + 1.7 kg per inch |
| Miller (1983) | 56.2 kg + 1.41 kg per inch | 53.1 kg + 1.36 kg per inch |
| Hamwi (1964) | 48 kg + 2.7 kg per inch | 45.5 kg + 2.2 kg per inch |
Worked Example: A Man of 5 Feet 10 Inches
That is 10 inches over 5 feet. Running all four formulas:
The four answers span 70.3 kg to 75.0 kg – a spread of 4.7 kg for the same person. None of them is wrong; they were derived from different datasets for different purposes.
That spread is the most useful thing about running all four. It demonstrates that ‘ideal weight’ is a range, not a point, even according to the formulas themselves.
| Formula | Calculation | Result |
|---|---|---|
| Devine | 50 + (2.3 x 10) | 73.0 kg |
| Robinson | 52 + (1.9 x 10) | 71.0 kg |
| Miller | 56.2 + (1.41 x 10) | 70.3 kg |
| Hamwi | 48 + (2.7 x 10) | 75.0 kg |
Worked Example: A Woman of 5 Feet 5 Inches
Five inches over 5 feet:
Here the spread is 56.5 kg to 59.9 kg, or 3.4 kg. Again, a range rather than a single number – and notably, all four sit in the lower half of the healthy BMI range for that height.
| Formula | Calculation | Result |
|---|---|---|
| Devine | 45.5 + (2.3 x 5) | 57.0 kg |
| Robinson | 49 + (1.7 x 5) | 57.5 kg |
| Miller | 53.1 + (1.36 x 5) | 59.9 kg |
| Hamwi | 45.5 + (2.2 x 5) | 56.5 kg |
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How This Compares to a Healthy BMI Range
A more useful approach for most people is to work out the weight range corresponding to a healthy BMI of 18.5 to 24.9 at your height. Multiply each threshold by your height in metres squared.
Comparing the two approaches for our examples:
The BMI range is considerably wider, and the formula results sit inside it – toward the middle for the man, toward the lower end for the woman.
For most purposes the wider range is the more honest answer. Healthy weight is not a single point that becomes unhealthy a kilogram either side. The formulas produce precise-looking numbers, and that precision is largely illusory.
| Formula Range | Healthy BMI Range | |
|---|---|---|
| Man, 5’10” (1.78 m) | 70.3 – 75.0 kg | 58.5 – 78.7 kg |
| Woman, 5’5″ (1.65 m) | 56.5 – 59.9 kg | 50.4 – 67.9 kg |
Note
This article is general information, not medical advice. Calculators give population-level estimates and cannot account for your individual health, medical history, or body composition. Speak to a doctor or registered dietitian before making significant changes to your diet, exercise, or weight.
So Where Does Age Come In?
Age is absent from all four equations, but it genuinely affects what a healthy weight looks like. The effect operates through body composition rather than through the number on the scale.
From roughly the age of 30, adults lose muscle mass progressively – a process called sarcopenia – unless they actively resist it with strength training and adequate protein. Fat mass tends to increase over the same period, and it redistributes toward the abdomen.
The consequence is that an unchanged weight over twenty years usually conceals a real change in composition: less muscle, more fat, at the same number.
- Muscle mass declines by roughly 3-8% per decade after 30, accelerating after 60.
- Fat distribution shifts toward the abdomen, which carries higher metabolic risk.
- Bone density declines, particularly after menopause.
- Height decreases slightly with age, which mechanically raises BMI even at a stable weight.
Some research suggests slightly higher BMI is associated with better outcomes in older adults, partly because a small reserve is protective during illness. This is why single-number targets become less appropriate with age, not more.
What These Formulas Cannot See
Height and sex are two inputs. Quite a lot is missing.
- Muscle mass. A trained person will exceed every formula result while being lean and healthy.
- Frame size. Skeletal structure varies meaningfully between individuals of the same height.
- Body composition. Two people at the same weight can have very different fat and muscle proportions.
- Ancestry. Healthy weight ranges and risk thresholds differ across populations.
- Health status. Existing conditions change what is appropriate, sometimes substantially.
A practical way to use these numbers: treat the formula result as the centre of a range rather than a target, check it against your BMI range, and add a waist measurement. If your waist is under half your height, that is a stronger signal of health than hitting any specific weight.
A More Useful Approach
If the goal is health rather than a number, these measures carry more information than ideal body weight does:
The last row is worth emphasizing. Cardiorespiratory fitness and strength predict health outcomes independently of body weight, and improving them is achievable regardless of whether you ever reach a formula’s ideal figure.
| Measure | Target | Why It Is Better |
|---|---|---|
| Waist-to-height ratio | Below 0.5 | Captures abdominal fat, the highest-risk kind |
| Body fat percentage | Sex-appropriate range | Distinguishes muscle from fat |
| Waist circumference | Below 94 cm men / 80 cm women | Simple and clinically validated |
| Strength and fitness markers | Improving over time | Predicts outcomes independently of weight |
Conclusion
Ideal body weight formulas give a quick reference point from height and sex, and running all four is more informative than running one – the spread between them shows how imprecise the concept is. For a 5’10” man the answers range from 70.3 kg to 75.0 kg.
Despite the common framing, none of these formulas use age. Age matters through body composition instead: muscle declines and fat redistributes, so the same weight means something different at 55 than at 25. For most people, a healthy BMI range combined with a waist measurement is a more useful target than any single ideal weight figure.
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Get your own figure in seconds – enter your height and sex to see your estimated ideal weight range.
Frequently Asked Questions
What is the formula for ideal body weight?
The most widely used is the Devine formula: 50 kg plus 2.3 kg per inch over 5 feet for men, and 45.5 kg plus 2.3 kg per inch for women. Three other formulas – Robinson, Miller and Hamwi – use the same structure with different constants and give results that can differ by several kilograms.
Do ideal weight formulas account for age?
No. All four standard formulas use only height and sex. Age does affect healthy body composition – muscle mass declines and fat redistributes toward the abdomen from around 30 onwards – but it is not an input to these equations.
Which ideal weight formula is most accurate?
None is definitively more accurate, because they were derived from different datasets for different clinical purposes. Devine is the most widely used, largely because it became standard for drug dosing. Running all four and treating the spread as a range is more informative than picking one.
Is ideal body weight the same as a healthy weight?
No. Ideal body weight formulas produce a single figure, while healthy weight is a range. The BMI-derived healthy range is considerably wider – for a 5’10” man it spans roughly 58.5 to 78.7 kg, compared with 70.3 to 75.0 kg from the formulas.
What should I use instead of ideal body weight?
A healthy BMI range for your height, combined with a waist measurement, gives a better picture. Waist-to-height ratio below 0.5 is a simple and well-validated target. Fitness and strength markers also predict health outcomes independently of what you weigh.
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