Ideal Weight Calculator

Imagine you are a 1970s pharmacist trying to figure out how much of a drug to give a patient. You cannot scan their body composition — you need a fast, repeatable rule based on height and sex. That is exactly why ideal body weight formulas exist. They were designed as clinical shortcuts, not precision health targets, and they have been in continuous medical use ever since.

Each of the four formulas starts from a base weight at exactly 5 feet tall, then adds a fixed amount per inch above that. The Devine formula — published in 1974 and still the most cited — uses 50 kg as the male base with 2.3 kg added per inch over 5 feet. The female version starts at 45.5 kg with the same 2.3 kg increment. Robinson, Miller, and Hamwi use slightly different base values and per-inch multipliers, which is why they produce slightly different results for the same height.

The range this calculator shows is the span from the lowest to the highest formula result. A narrow range means the formulas largely agree. A wider range at taller heights reflects the fact that the formulas were not designed for people well above or below average height — the linear assumption stretches less convincingly at the extremes. The midpoint gives you a single reference number if you need one, but the full range is the more honest answer.

Use this calculator when you want a quick reference point for a healthy weight range based on height and sex, when you are preparing for a conversation with a doctor or dietitian and want a baseline number to discuss, or when you are working in a clinical context that requires an IBW estimate for drug dosing or nutritional assessment.

Do not rely solely on this calculator if you are an athlete or have significantly above-average muscle mass — the formulas will underestimate your appropriate weight. Do not use it for children or adolescents under 18, where growth percentile charts are the correct tool. And do not use it as a substitute for a full body composition assessment if you are making a significant health or training decision. A DEXA scan, hydrostatic weighing, or even a well-administered skinfold test gives far more actionable information than any height-and-sex formula.

This calculator is appropriate for general orientation and clinical quick-checks. It is not appropriate as the sole basis for a weight management program, eating disorder treatment, or surgical candidacy assessment.

The most common mistake is treating the formula result as a weight loss goal. These formulas produce population-level reference values, not personal prescriptions. A 6-foot-tall person with above-average muscle mass who weighs 30 lbs above the Devine midpoint may already be at an excellent body composition. Using the formula result as a hard target without considering fitness level, muscle mass, or fat distribution can lead to chasing a number that is wrong for that individual.

A second frequent error is applying these formulas to heights far from the 5-foot baseline. Because the formulas are linear, they extrapolate in a straight line indefinitely. For a 4 ft 8 in adult, the formula can return a weight that is physiologically implausible. Similarly, very tall people often find the formula returns a target well below a lean, muscular weight they already maintain. The boundary warnings in this calculator flag heights where results become unreliable.

A third mistake, specific to clinical users, is confusing Actual Body Weight, Ideal Body Weight, and Adjusted Body Weight. Drug dosing protocols often specify which weight to use for a given medication. Using this calculator to get the IBW and then applying it where Adjusted Body Weight is required — common for obese patients on certain IV antibiotics — can result in dangerous underdosing or overdosing. Always verify which weight type a dosing protocol specifies.

All four formulas follow the same structure: Base Weight (kg) + Per-Inch Increment x Inches Above 60.

Devine (1974): Males 50 + 2.3 per inch; Females 45.5 + 2.3 per inch. Robinson (1983): Males 52 + 1.9 per inch; Females 49 + 1.7 per inch. Miller (1983): Males 56.2 + 1.41 per inch; Females 53.1 + 1.36 per inch. Hamwi (1964): Males 48 + 2.7 per inch; Females 45.5 + 2.2 per inch.

Results in kilograms are converted to pounds using the exact factor 2.20462. For a 5 ft 11 in male using the Devine formula: 11 inches over 5 feet gives 50 + (2.3 x 11) = 75.3 kg, which converts to approximately 166 lbs. The range and midpoint are then computed across all four formula outputs for that sex and height combination.

Note that none of the formulas include age, weight, frame size, or body composition as inputs. This is a known limitation — it reflects the original design intent of providing a rapid clinical approximation, not a precise physiological target.

The linear structure of all four formulas creates a systematic underestimation problem at height extremes. The per-inch increment was derived from population data clustered near average height. As height deviates further from 5 feet, the linear assumption diverges from actual population weight distributions, which follow a more complex curve. Clinical pharmacologists sometimes apply a correction: for heights significantly below 5 feet, some protocols substitute actual body weight when it is lower than the IBW calculation. The formulas also implicitly assume a medium frame — neither the Devine nor the Robinson formula has a frame-size adjustment, though Hamwi was originally described with a plus-or-minus 10 percent frame adjustment that is rarely applied in practice.