Which ideal weight formula is most accurate?
No single formula is definitively most accurate, and that's a feature, not a bug — each was calibrated on different reference data. Devine is most commonly used in clinical drug dosing but tends to underestimate for very tall people and overestimate for very short ones. Robinson is often considered more balanced for average frames, and Miller usually lands highest because it was based on more recent population data. The average of all four, or the BMI healthy range, is generally a better target than any single number.
Why do the formulas give different results?
Each formula was developed using different data sets, time periods, and methodologies. Hamwi (1964) came from clinical observations in a diabetes-care monograph. Devine (1974) was published as a drug-dosing tool based on insurance actuarial data, not direct health measurements. Robinson (1983) modified Devine's per-inch rate, and Miller (1983) used more recent population data. The variation you see is the legitimate uncertainty in trying to map height to a single 'ideal' weight.
Is there one 'perfect' ideal weight I should aim for?
No. Health exists across a range of weights, which is why the BMI-based healthy range (BMI 18.5–24.9) is usually a more useful target than any single formula output. Being within 10–15% of the four-formula average while maintaining good health markers — blood pressure, lipids, fitness, energy — is what matters in practice. Anchoring on one number from one formula misses the point.
Should muscle mass change how I read these numbers?
Yes. The Devine and Hamwi formulas were built to approximate lean body mass for drug dosing, not to predict optimal weight for athletes or resistance-trained adults. If you have visibly low body fat and significant muscle, every formula here will underestimate your healthy weight. Use body-fat percentage, waist circumference, or a DEXA scan as the primary reference and treat the formula output as a floor, not a ceiling.
What's a healthy weight range — and is it different from ideal weight?
A healthy weight range is the band of weights that puts your BMI between 18.5 and 24.9, which the CDC, NIH, and WHO use as the Normal-weight zone for adults. This calculator computes that range alongside the four formula results. It's broader (often 15–25 kg wide) and generally a more clinically useful target than any single formula number, which represents a point estimate of lean body mass rather than a recommended weight.
Why are these formulas based on height alone?
They were designed for fast bedside calculation — in 1964 or 1974, a pharmacist or nurse needed a back-of-the-envelope estimate of lean body mass to dose a drug. Height is easy to measure once and stays constant, so it became the input variable. Modern research clearly shows that weight at a given height depends on muscle mass, bone density, fat distribution, age, sex, and ethnicity, but those weren't variables the original formulas tried to capture.
Should I focus on weight or body composition?
For most adults, body composition is the more informative target. Two people of identical height and 'ideal' weight can have radically different body-fat percentages, and the higher-body-fat person carries higher cardiometabolic risk despite hitting the same scale number. Use these formulas to confirm you're roughly in the healthy band, then track waist circumference, body-fat percentage, and fitness markers as your primary signals.
I'm athletic and weigh more than my 'ideal weight.' Is that bad?
Not at all. These formulas don't account for muscle mass. Athletes and regular exercisers often exceed ideal weight calculations while being very healthy. If you have significant muscle mass, your actual healthy weight is likely higher than these formulas suggest — check body-fat percentage or waist-to-height ratio instead.
What if I'm short or very tall?
These formulas are least accurate at height extremes. For people under 5 feet or over 6'2", the formulas may significantly under- or over-estimate ideal weight, because they extrapolate a linear per-inch rate well beyond the reference data they were fit on. The BMI healthy range scales more proportionally with height and is usually the better reference at the extremes.
How do I determine my frame size?
The simplest method is the wrist test: wrap your thumb and middle finger around your wrist at the narrowest point. If they overlap, you have a small frame. If they just touch, medium frame. If they don't meet, large frame. For more precision, measure wrist circumference in inches and divide by height in inches — published reference charts then map that ratio to small/medium/large.
Why don't these formulas consider age?
They were designed for simplicity in clinical settings. While body composition changes with age — adults tend to lose muscle and gain fat after about age 50 — the basic height-weight relationship the formulas model doesn't change dramatically. Some experts and recent meta-analyses suggest that slightly higher weights (BMI 25–27) may actually be protective in adults over 65, so don't aim lower than the formula average if you're in that group.
Are these formulas used in real medicine?
Yes — primarily for drug dosing rather than as fitness targets. The Devine formula in particular is embedded in pharmacy references for aminoglycosides, vancomycin, and other drugs cleared by lean body mass, and the American Society of Health-System Pharmacists still cites it. ICU clinicians also use IBW to set lung-protective tidal volumes in mechanical ventilation. None of these uses positions IBW as a weight a healthy person should try to hit.
