Ideal Body Weight Calculator

The four formulas explained

All four formulas share the same structure: a base weight at 5 feet, plus a fixed amount per inch above 5 feet. They differ in the base weight and per-inch increment. In many practical calculator implementations, heights below 5 feet are treated cautiously because the original formulas were built around the 5-foot anchor.

Hamwi (1964) — Men: 48 kg + 2.7 kg/inch over 5 ft; Women: 45.5 kg + 2.2 kg/inch over 5 ft. Designed for insulin dosing.

Devine (1974) — Men: 50 kg + 2.3 kg/inch over 5 ft; Women: 45.5 kg + 2.3 kg/inch over 5 ft. Still widely cited in pharmacy.

Robinson (1983) — Men: 52 kg + 1.9 kg/inch; Women: 49 kg + 1.7 kg/inch. Proposed as a refinement.

Miller (1983) — Men: 56.2 kg + 1.41 kg/inch; Women: 53.1 kg + 1.36 kg/inch. A second 1983 update.

IBW versus a healthy BMI range

An IBW calculator gives point estimates. A healthy BMI range gives a corridor of weights that correspond to BMI 18.5 to 24.9 for the same height. Looking at both together is usually more useful than chasing a single 'ideal' number.

That comparison matters because the formula spread can be several kilograms wide. If the four formulas cluster inside a healthy BMI corridor, the result is easier to interpret. If your current weight is outside that corridor, you still need clinical context, body-composition context, and common-sense judgment.

Target BMI reference and frame-size context

Many people use an ideal weight calculator because they really want to compare several reference ideas at once: the classic ideal body weight formulas, a healthy weight range by height, and a selected BMI reference such as BMI 22 or BMI 24. This calculator keeps those ideas separate so the result does not pretend that one target is medically perfect.

The target BMI field solves the same-height weight implied by your chosen BMI value. It is useful for comparison because BMI uses only height and weight, while the IBW formulas use height and sex. If the selected BMI reference and the formula average are close, the result is easier to interpret. If they disagree, that disagreement is a signal to look at body composition, frame size, training status, and clinical context before choosing any goal.

Frame size is deliberately treated as interpretation context rather than a hidden formula adjustment. Some ideal weight discussions mention small, medium, or large frames, but the classic equations themselves still do not measure wrist circumference, skeletal breadth, muscle mass, or fat distribution. A larger or more muscular adult can sit above the formula average without that automatically making the weight unhealthy.

How to compare your current weight with IBW

If you know your current body weight, compare it with both the formula average and the healthy BMI range at the same height. The gap from the average tells you how far your current weight sits from the center of the formula cluster, while the BMI corridor shows whether that current weight is broadly below, within, or above a common adult reference range.

This does not turn IBW into a weight-loss prescription. It simply gives you more context than a bare formula result. Someone with higher lean mass, a larger frame, or a sport-specific build may sit above a formula average and still have acceptable health markers.

Worked examples and formula spread

Take a 175 cm adult male. The classic formulas land in a narrow but noticeable band, with some formulas lower and some higher. That spread is expected because each equation came from a different population and assumption set.

For a 160 cm adult female, the same thing happens: the four formulas stay in roughly the same neighbourhood, but they do not produce one magic answer. That is why a strong ideal weight calculator should show the range across formulas, not just one headline figure.

Why IBW has limitations

These formulas use only height and sex. They ignore frame size, muscle mass, age, ethnicity, edema, amputation, and most of the real-world factors that change what a healthy body weight looks like.

They are also adult-oriented heuristics. They are not the right tool for children, teens, pregnancy, frailty, or specialist clinical settings where another weight definition such as predicted body weight or adjusted body weight may be required.