About the Ideal Weight Calculator
An ideal weight calculator returns a target weight range based on classical clinical formulas — Devine, Hamwi, Robinson, Miller. These formulas were originally developed for medication dosing, not as health goals, but they're widely used as benchmarks. The honest interpretation: "ideal" weight is more usefully thought of as a range than a single number, and depends meaningfully on body composition, frame, age, and individual health context.
Where the formulas come from
The Devine formula (1974) was developed for clinical use, particularly for calculating drug dosages where lean body mass mattered. The original Devine equation: men 50 kg + 2.3 kg per inch over 5 ft; women 45.5 kg + 2.3 kg per inch over 5 ft. The Hamwi formula (1964) is similar with slightly different coefficients. Robinson (1983) and Miller (1983) refined the constants based on later population data.
These formulas pre-date BMI's adoption as the dominant population-level metric and don't account for body composition at all. Two adults of the same height and same Devine-ideal weight can have radically different muscle and fat distributions. Use the result as a starting reference, not a goal.
Why the formulas disagree (and which to trust)
Different formulas can give ideal weights that differ by 5–10 kg for the same person. This isn't a flaw in any one formula — it's a reflection of the fact that there's no single, scientifically valid "ideal" weight. The healthiest weight for a given height varies with frame size, body composition, age, and individual genetic factors.
For most adults, a more useful target is to be within the BMI healthy range (18.5–24.9), with body fat percentage in the healthy range (10–22% men, 20–32% women), and waist circumference under high-risk thresholds (40" men, 35" women). Whether you're at the low or high end of "ideal weight" within that healthy range matters far less than whether you're in it at all.
Frame size, age, and the ranges that actually matter
Frame size (small, medium, large) was traditionally estimated from wrist or elbow circumference relative to height. Larger-framed individuals often have a higher healthy weight than the formulas suggest because they carry more bone and connective tissue. For a small-framed person, the lower end of the formula range fits; for a large-framed person, the higher end often does.
Healthy weight ranges shift slightly with age. The classic Metropolitan Life weight tables — long the reference — have been updated to reflect that modestly higher weights may be appropriate for older adults than for young adults of the same height. Don't aggressively pursue 25-year-old weight at 60.
When ideal weight is a clinical question, not a vanity question
For people in higher BMI categories with metabolic dysfunction (Type 2 diabetes, dyslipidemia, hypertension), even modest weight loss (5–10% of starting weight) often produces meaningful improvements in disease markers — sometimes more than reaching any specific target weight. The "first 10" matter most.
Conversely, for people at low body weight, gaining can be as health-relevant as losing for those above. Older adults especially benefit from preserving lean mass and maintaining sufficient body weight; involuntary weight loss in older adults is associated with worse outcomes. Ideal weight is highly context-dependent.
Formula
- Result = Ideal body weight in kilograms
- inches over 5 ft = Height in inches minus 60
Worked examples
Man, 5'10" (70 inches)
Devine: 50 + 2.3 × 10 = 73 kg (~161 lb). Hamwi: 48 + 2.7 × 10 = 75 kg (~165 lb). Robinson: 52 + 1.9 × 10 = 71 kg (~157 lb). Range across formulas: 71–75 kg (157–165 lb).
Woman, 5'5" (65 inches)
Devine: 45.5 + 2.3 × 5 = 57 kg (~126 lb). Hamwi: 45.5 + 2.2 × 5 = 56.5 kg (~125 lb). Robinson: 49 + 1.7 × 5 = 57.5 kg (~127 lb). Range: ~125–127 lb.
BMI healthy range for the same heights
5'10" man: BMI 18.5–24.9 covers 129–174 lb. 5'5" woman: 111–150 lb. The BMI-healthy range is wider than any single formula's "ideal" — which is why most clinicians treat the formulas as starting points within the broader healthy range, not as targets in themselves.
Frequently asked questions
Which ideal weight formula is most accurate?
None is definitively more accurate — they were all developed for different clinical purposes and use different population data. For practical use, treat them as a range rather than a target. The lower end suits smaller-framed individuals; the higher end suits larger frames and more muscular bodies.
Should I aim for my ideal weight from a calculator?
Use it as a reference, not a goal. A more useful framework: aim to be within the BMI healthy range (18.5–24.9) with body fat percentage in the healthy range and waist circumference below high-risk thresholds. Within that broader range, where exactly you settle is a personal and medical question, not a formula one.
Why is my ideal weight different in different formulas?
The formulas use different constants developed from different reference populations at different times. Their "agreement" within a few kilograms is roughly the precision of any of them. Use the average or the range across formulas, not any single result.
Does ideal weight change with age?
Slightly. Older adults often have a slightly higher healthy weight range than young adults of the same height, partly because some research suggests modest elevation may be protective in older populations. More important than weight in older age is preserving lean mass and avoiding involuntary weight loss.
Does muscle mass affect ideal weight?
Yes — significantly. Muscular individuals can be well above the formulas' "ideal" weight while having very low body fat and excellent metabolic health. For athletes and resistance-trained individuals, body fat percentage and waist circumference are more informative than ideal-weight formulas.
Are ideal-weight formulas useful for medication dosing?
Yes — that's their original purpose. Many drugs (especially aminoglycoside antibiotics, some chemotherapy agents) are dosed based on lean body mass, and Devine in particular remains widely used in clinical pharmacy for this. The formulas are more validated for this purpose than as health-goal targets.