Ideal Body Weight Formulas: Devine, Hamwi, and What They Really Tell You
Ideal body weight formulas give a quick target number from your height, but they were built for a narrow purpose. Here is how they work and where they fall short.
The idea of an ideal body weight is appealing because it turns a complicated question into a single number. Type in your height, get back a weight, and you have something to aim for. The two formulas you will meet most often are Devine and Hamwi, and both do exactly that. What most people never hear is that these formulas were never meant to describe a healthy or attractive body. They were tools for very specific clinical problems, and that history explains both their usefulness and their limits.
How the Devine and Hamwi formulas work
The Hamwi formula came first, published in 1964 as a quick bedside way to estimate weight. For men it assigns 48 kilograms for the first 152 centimeters of height, then adds 2.7 kilograms for every additional 2.5 centimeters. For women it starts at 45.5 kilograms and adds 2.2 kilograms per 2.5 centimeters. The Devine formula, from 1974, works the same way with slightly different numbers: 50 kilograms plus 2.3 kilograms per inch over five feet for men, and 45.5 kilograms plus the same increment for women.
- Devine, men: 50 kg + 2.3 kg for each 2.5 cm above 152 cm.
- Devine, women: 45.5 kg + 2.3 kg for each 2.5 cm above 152 cm.
- Hamwi, men: 48 kg for the first 152 cm + 2.7 kg per 2.5 cm.
- Hamwi, women: 45.5 kg for the first 152 cm + 2.2 kg per 2.5 cm.
What the formulas leave out
Notice that height is the only input. Two people who are exactly the same height get the same ideal weight, even if one is a lean marathon runner and the other carries far more fat and less muscle. The formulas cannot see body composition. A muscular person can weigh well above their formula number and be very healthy, while someone with low muscle mass can sit right on target and still carry excess fat.
- Muscle weighs more than fat for the same volume, so athletes read as overweight.
- Frame size and bone density are ignored completely.
- Age related changes in muscle and fat are not accounted for.
- The formulas were validated mostly on adult populations, not children or the very elderly.
How to use the number sensibly
Treat an ideal body weight figure as a rough anchor for planning, not a finish line. It is fine for setting a broad direction, but pair it with a waist to height check and, if you can, a body fat estimate. Progress in strength, energy, and everyday movement matters more than landing on one specific figure that a formula from decades ago printed for you.