Ideal Weight Calculator
Estimate your "ideal" reference body weight from your height, biological sex, and body frame size using the Devine formula — originally created in 1974 for pharmacological dose calculation and still used clinically today. Useful as a rough planning anchor, but not a personal weight goal: it ignores muscle mass, age, and individual physiology.
About this calculator
The Devine formula returns ideal body weight (IBW) in kilograms from height in inches: IBW (male) = 50 + 2.3 × (height_in − 60), IBW (female) = 45.5 + 2.3 × (height_in − 60), with height_in = height_cm ÷ 2.54. This calculator adds a body frame multiplier — large 1.1, medium 1.0, small 0.9 — to reflect that a wider skeletal frame supports proportionally more weight at the same height. The complete formula is: IBW = (50 if male else 45.5) + 2.3 × ((height_cm ÷ 2.54) − 60) × frame_multiplier. Dr. B.J. Devine published the equation in a 1974 hospital pharmacy newsletter for calculating loading doses of gentamicin in obese patients — the IBW was the "dosing weight" used to avoid overdosing in patients whose actual weight was dominated by adipose tissue. It was never validated as a fitness target or a healthy-weight reference, but became the most-cited IBW formula in clinical pharmacology because it was simple and produced reasonable estimates. Alternatives include Robinson (1983), Miller (1983), Hamwi (1964), Broca (1871), and the WHO's BMI-based "healthy weight range" approach (BMI 18.5–24.9 × height_m²), which yields a range rather than a single number. Edge cases: the formula breaks down at very short statures — for an adult under 5 feet (152 cm), the (height_in − 60) term goes negative, subtracting weight from the baseline; clinical practice typically caps this at the baseline value (50 kg / 45.5 kg). It also has no adjustment for age (older adults tend to have less lean mass and can be healthy at lower weights), ethnicity (BMI-equivalent IBW differs across populations), or muscularity (an elite male sprinter at 175 cm might weigh 80 kg of mostly muscle while the Devine IBW is 71 kg). Treat the output as a clinical reference point, not a personal target.
How to use
Example 1 — Average-frame man. You are male, 180 cm tall, medium frame. Convert height: 180 ÷ 2.54 ≈ 70.87 inches. Base IBW = 50 + 2.3 × (70.87 − 60) = 50 + 2.3 × 10.87 = 50 + 25.00 = 75.0 kg. Apply medium-frame multiplier (1.0): 75.0 × 1.0 = 75.0 kg. ✓ The Devine IBW for this man is about 75 kg. For comparison, the BMI 18.5–24.9 healthy range for 180 cm is 60–81 kg — Devine sits comfortably in the upper half of that band. Example 2 — Large-frame woman, shorter stature. You are female, 162 cm tall, large frame. Convert height: 162 ÷ 2.54 ≈ 63.78 inches. Base IBW = 45.5 + 2.3 × (63.78 − 60) = 45.5 + 2.3 × 3.78 = 45.5 + 8.69 = 54.2 kg. Apply large-frame multiplier (1.1): 54.2 × 1.1 ≈ 59.6 kg. ✓ A small-frame woman at the same height would land at 54.2 × 0.9 ≈ 48.8 kg — a 10.8 kg swing across the frame-size options, which is the formula honestly admitting how much skeletal-frame variation it cannot directly measure.
Frequently asked questions
What is the Devine formula and why is it still used?
The Devine formula was published by Dr. B.J. Devine in 1974 in a hospital pharmacy newsletter as a tool for calculating drug doses in patients whose body weight was dominated by adipose tissue, where dosing on actual weight would risk toxicity. It set IBW at 50 kg (men) or 45.5 kg (women) for a person 5 feet tall, then added 2.3 kg per inch above that. It became the dominant IBW formula in clinical pharmacology because it was simple, produced plausible numbers, and got embedded in hospital protocols and dosing software before alternatives like Robinson or Miller could displace it. It survives today not because it is the most accurate (it slightly overestimates IBW for tall people and underestimates for short ones compared to newer formulas) but because medical guidelines are slow to change and physicians are trained on it. For personal fitness or weight goals, modern guidance prefers a BMI range or a body-composition target over any single IBW number.
How do I determine my body frame size?
The most accurate clinical method is elbow breadth — measure the distance between the two prominent bones on either side of your elbow with the arm bent at 90°, using calipers, and compare to age- and height-specific reference tables (the Metropolitan Life tables are the classic source). A practical proxy is wrist circumference: divide your height (cm) by your wrist circumference (cm); for men, ratios above 10.4 indicate a small frame, 9.6–10.4 medium, below 9.6 large; for women, the cutoffs are 11.0 and 10.1. The 10% adjustment used by this calculator is a deliberately blunt instrument — actual frame-size effects on healthy weight can be larger in extreme cases. If you are not sure, "medium" is the right default; the answer is then comparable to most published Devine IBW tables.
How does ideal weight differ from a healthy BMI range?
Ideal body weight returns a single number; a healthy BMI range gives you a band. For 175 cm height, BMI 18.5–24.9 corresponds to roughly 57–76 kg — a 19 kg range that explicitly acknowledges that many different weights can all be healthy for the same height depending on body composition, age, and muscle mass. The Devine IBW for the same 175 cm male sits at about 72 kg, near the top of that range. WHO, NHS, and CDC guidelines have moved toward the BMI-range framing for healthy-weight communication precisely because IBW formulas create the false impression that there is one correct weight to hit. Use the BMI range to decide whether your weight is in a healthy zone, and use IBW only as a single-point reference (clinical dosing, comparison to historical norms, etc.).
What are the most common mistakes people make with ideal weight calculators?
Treating the output as a personal target rather than a reference — the Devine formula was never validated as a fitness goal. Forgetting that body composition matters more than total weight; a 75 kg person at 15% body fat is in a very different metabolic state from a 75 kg person at 30%, even though IBW would treat them identically. Picking the wrong frame size — most people guess "medium" when their actual elbow breadth would put them in the large or small bucket, swinging the result by 10–15%. Comparing your IBW to a friend's or partner's and drawing conclusions — IBW only meaningfully compares within the same age, sex, and ancestry group. And applying the formula at extreme heights (well below 150 cm or above 200 cm) where the linear extrapolation breaks down and produces nonsensical numbers.
When should I not use this calculator?
Skip it during pregnancy and breastfeeding — your weight is supposed to be in flux, and any IBW for the non-pregnant state does not apply. Skip it for children and adolescents under 18 — paediatric healthy weight is assessed against age- and sex-specific BMI percentile charts, not an adult formula. It is unreliable at the extremes of stature: under about 150 cm or over about 200 cm the formula extrapolates beyond the range of bodies it was derived from. It is also wrong for amputees (you would need to subtract the missing limb mass from any target weight), people with significant muscle mass relative to height (athletes, bodybuilders, manual labourers), and frail older adults with sarcopenia (where holding "ideal weight" can actually be unhealthy). For setting a personal weight goal in a healthy way, talk to a registered dietitian who can integrate body composition, family history, fitness level, and goals — no single-number formula captures all of that.