Your ideal weight,
four ways.

Field guide

What “ideal weight” really means.

Ideal Body Weight (IBW) is a target weight derived from your height. The concept dates back to the actuarial height/weight tables published by Metropolitan Life Insurance in the 1940s, but the formulas in everyday use today were written between 1964 and 1983, all of them as quick clinical rules of thumb for drug dosing and ventilator settings, not as nutritional ideals.

That history is the most important thing to remember about IBW: it is a clinical estimate, not a personalised optimum. The four formulas below were never validated against long-term health outcomes; they were chosen because they produced sensible numbers for clinicians who needed a quick weight estimate when a patient could not be weighed.

The Hamwi formula (1964)

The original. G. J. Hamwi proposed it as a clinical shorthand at the Ohio State University College of Medicine. Hamwi was also the first to introduce the frame-size correction: add 10% for a large frame, subtract 10% for a small frame, which most modern calculators still expose. The Hamwi slope is the steepest of the four, so at very tall heights it produces the highest IBW.

The Devine formula (1974)

By far the most widely cited. Dr. B. J. Devine published this formula in a clinical-pharmacology paper as a quick rule for gentamicin dosing. It was never formally validated against population averages, but it became standard clinical practice in the United States and remains the IBW of record for many drug-dosing protocols today.

The Robinson formula (1983)

Robinson and colleagues refitted the Devine slope against actuarial life-insurance tables, the same dataset Metropolitan Life had been using since the 1940s. Robinson tends to give slightly higher targets at average heights, and slightly lower targets at very tall heights, than Devine.

The Miller formula (1983)

The same year as Robinson but using the gentlest slope of the four. Miller produces noticeably lower targets above 5′10″ and is sometimes preferred for very tall patients where Devine and Hamwi tend to over-estimate.

Why the BMI range is usually a better reference

All four classic formulas produce a single number for ideal weight at a given height. That misses the most important fact about human variation: healthy weight is a range, not a point. Two adults of identical height can differ by 20 kg and both be metabolically healthy if the difference is muscle, bone density, or natural frame.

The BMI healthy band of 18.5 to 24.9, derived from population-health data, not from anaesthesia practice — spans roughly a 35% range in body weight at any given height. That width is the feature, not a bug. For most modern, non-clinical purposes, the BMI band is the more defensible “ideal” reference. The formulas above are still useful as historical landmarks and for clinical drug-dosing contexts where a single number is required.

Frame size: measuring it properly

The Hamwi adjustment of ±10% requires a frame-size estimate. Two methods are in common use:

• Wrist circumference vs. height. Wrap a tape around your wrist just past the bony bump (styloid process). Calculate height ÷ wrist circumference, both in the same units. For men: >10.4 small, 9.6–10.4 medium, <9.6 large. For women: >11 small, 10.1–11 medium, <10.1 large.
• Elbow breadth. Bend your forearm 90° and measure the distance between the two prominent bones at the elbow with calipers. Compare against published tables by sex and height. More rigorous, less practical.

Where IBW formulas break down

• Below 5 ft (152.4 cm): every classic formula has the form “base + slope × inches over 5 ft.” Below the 5-ft anchor, results approach zero or go negative. Use the BMI band instead.
• Athletes and lifters. A muscular athlete at 90 kg and 12% body fat is metabolically healthier than the IBW formulas would suggest. Body composition matters more than total weight.
• Older adults. Mortality data suggest older adults do better at the upper end of the BMI healthy range than at the lower end. The same number that represents “ideal” at 30 may be too low at 70.
• Children and teenagers. Growth changes the relationship between height and weight constantly. For under-18s, paediatric BMI percentile charts are the correct reference, not adult formulas.

Worked example

A 5′10″ (178 cm) male wants to know his ideal weight. Inches over 5 ft = 10.

• Hamwi: 48 + 2.7 × 10 = 75 kg
• Devine: 50 + 2.3 × 10 = 73 kg
• Robinson: 52 + 1.9 × 10 = 71 kg
• Miller: 56.2 + 1.41 × 10 = 70.3 kg

The four-formula mean is 72.3 kg. The BMI healthy band at 1.78 m runs from 18.5 × 1.78² ≈ 58.6 kg to 24.9 × 1.78² ≈ 78.9 kg — a 20 kg spread that comfortably contains all four formula results.

How to actually use these numbers

Treat the four-formula average as a single landmark, not a target. The healthy BMI band is the practical reference for most non-clinical decisions. If your current weight sits inside the BMI band and your blood pressure, fasting glucose, and waist circumference are normal, the question of which IBW formula matches your weight is not clinically interesting.

If your current weight sits well outside the BMI band and you want a target to plan around, pick a value at the edge of the band closest to where you are now — losing or gaining to the boundary is more sustainable than aiming for a single point in the middle.

Disclaimer

This calculator is an educational tool and not a substitute for professional medical advice. Ideal weight depends on individual circumstances — body composition, fitness, medical history, age. That no formula can capture. Discuss your weight with a clinician who can interpret the number in the context of your full health picture.