How the ideal weight calculator works
This calculator shows your ideal body weight from four established medical formulas (Robinson, Miller, Devine, Hamwi) alongside the healthy BMI range for your height. Rather than giving you a single "magic number," it shows the spread across formulas so you can see where legitimate medical opinion converges and where it differs.
Enter your age, sex, and height to get all results instantly. Expand "Advanced" to adjust for body frame size.
How to use it
- Enter your age and sex.
- Enter your height (the unit selector is grouped with the field).
- Read the ideal weight from each formula plus your healthy BMI range.
- Optionally expand Advanced to adjust for a small or large frame (±10%).
How ideal weight formulas are calculated
All four formulas follow the same structure: a base weight for a height of 5 feet (60 inches), plus an increment per inch above that.
The Healthy BMI Range shows the weight at which your BMI would be 18.5 (lower bound) and 25 (upper bound), calculated as BMI × height(m)².
Why the formulas disagree
Each formula was developed for a different purpose from different populations:
- Devine (1974) was created to calculate medication dosages, not body composition goals. It tends to give lower values, particularly for women.
- Hamwi (1964) comes from clinical nutrition and gives the highest values, particularly for taller men.
- Robinson and Miller (1983) were both developed to improve on Devine, using broader population data. They tend to cluster in the middle.
The disagreement is actually informative: it tells you that "ideal weight" is not a precise scientific concept. A range of 5–8 kg across formulas is typical and normal.
How to interpret the results
The most practical approach:
- Look at the range, not a single number. If all four formulas say 68–77 kg, your target zone is somewhere in that range.
- Compare against the healthy BMI range. If your formula results fall within the BMI range (18.5–25), you're in well-supported territory.
- Consider your body composition. Muscular people should aim for the higher end of the range (or beyond it). The formulas don't account for lean mass.
- Use frame size in Advanced if you know your build is notably smaller or larger than average. Small frame = aim for the lower end; large frame = the higher end.
Frame size adjustment
The optional frame size adjustment (in Advanced) scales all formula results by ±10%:
- Small frame: multiply by 0.9 (thinner bones, narrower build)
- Medium frame: no adjustment
- Large frame: multiply by 1.1 (wider build, heavier bones)
To determine your frame, measure your wrist circumference. For men over 165 cm: small < 16.5 cm, medium 16.5–19 cm, large > 19 cm. For women over 157 cm: small < 15.2 cm, medium 15.2–16 cm, large > 16 cm.
Why healthy BMI range is included
The formula-based weights and BMI-based range serve different purposes. The formulas give a point estimate based on statistical averages from the 1960s–1980s. The BMI range (18.5–25) represents the modern epidemiological consensus on the weight range associated with lowest mortality and disease risk. When formula results fall within the BMI range, you have strong convergent evidence. When they differ (usually at height extremes), the BMI range is more broadly validated.
Common mistakes to avoid
- Treating the number as an absolute target. These are statistical averages, not personal prescriptions. Two people of identical height can have very different healthy weights depending on muscle mass.
- Ignoring body composition. If you strength train and have above-average muscle, your healthy weight is higher than any formula predicts. Body fat percentage is more informative than scale weight for athletic people.
- Using Devine as a weight-loss goal. Devine consistently gives the lowest values because it was designed for drug dosing, not body composition. Don't chase it.
- Comparing across height units. The formulas are internally consistent in kg. If you switch to imperial, compare within that unit system.
Limitations
These formulas were developed from studies on Western adults in the mid-to-late 20th century. They may not reflect ideal weights for all ethnicities, body types, or age groups accurately. They don't account for muscle mass, bone density, or individual metabolic factors. For personalized guidance, a healthcare provider can assess body composition directly and consider your full health profile.
Frequently asked questions
Why do different formulas give different ideal weights?
Each formula was developed from different study populations at different times. Devine (1974) was originally for drug dosing, not body composition. Hamwi (1964) comes from clinical nutrition. Robinson and Miller (both 1983) refined earlier work with broader datasets. The range between them reflects genuine uncertainty — use the average as a guide, not an absolute target.
How do I determine my frame size?
The simplest method is wrist circumference relative to height. For men over 5′5″: small frame < 6.5″, medium 6.5–7.5″, large > 7.5″. For women over 5′2″: small < 6″, medium 6–6.25″, large > 6.25″. Alternatively, measure elbow breadth — a sports lab or doctor can do this precisely.
Are these formulas accurate for short or very tall people?
They work best between roughly 5′0″ and 6′4″ (152–193 cm). At extremes of height, the linear formulas over- or under-predict. For people under 5′0″, BMI-based ranges (18.5–24.9 applied to your height) may be more appropriate than these formulas.
Should I try to hit my exact ideal weight?
No. Treat the range across formulas as a healthy target zone, not a single magic number. Healthy weight depends on muscle mass, bone density, fat distribution, and metabolic markers (blood pressure, blood sugar, cholesterol) — not just a number on a scale. Someone at 10% above their 'ideal' with good body composition and health markers is perfectly healthy.
Do these formulas account for muscle mass?
No. All four formulas use only height and sex. They were designed for average body compositions and will underestimate ideal weight for muscular individuals. If you strength train regularly, your healthy weight is likely higher than these formulas suggest. Body fat percentage is a better metric for athletic people.
Why is the Devine formula used in medicine?
The Devine formula was originally developed to calculate drug dosages based on lean body weight. It became widely adopted in clinical settings for tidal volume calculations, creatinine clearance estimation, and other dose-dependent decisions. It wasn't designed as a body-weight goal, which is why it sometimes gives lower values than other formulas.