How is ideal weight worked out?
Ideal body weight (IBW) formulas were first made to dose medicines, and they are now a common reference for a healthy weight. Each starts from a base weight at 5 feet and adds a set amount for every inch above it, with different numbers for men and women. The calculator shows four classic formulas and the weight range for a healthy BMI, which is the broadest guide.
Example: for a man 5 ft 10 in tall, the formulas give 156.5 lb (Robinson), 155.0 lb (Miller), 160.9 lb (Devine) and 165.3 lb (Hamwi); the healthy BMI range is 128.9 to 174.2 lb.
The formulas
- Robinson (1983): men 52 kg + 1.9 kg per inch over 5 ft; women 49 kg + 1.7 kg
- Miller (1983): men 56.2 kg + 1.41 kg; women 53.1 kg + 1.36 kg
- Devine (1974): men 50 kg + 2.3 kg; women 45.5 kg + 2.3 kg
- Hamwi (1964): men 48 kg + 2.7 kg; women 45.5 kg + 2.2 kg
An ideal weight is a range
None of these formulas looks at muscle, frame size or where you carry fat, so treat them as a rough guide. A weight anywhere in the healthy BMI range, a waist under half your height and good fitness matter more than one exact number.
Frequently asked questions
Which formula is best?
None is clearly best. Devine is the most used in medicine; Robinson and Miller were later corrections of it. The average is a sensible middle.
Does age change my ideal weight?
The formulas don't use age. Many people gain some weight with age, and a weight at the upper end of the healthy range is often fine for older adults.
What about people under 5 feet?
The formulas were made for people of at least 5 feet; below that they subtract weight per inch and become less reliable.