Healthy Weight Range: A ±10% band around the Hamwi ideal. If your current weight falls inside this window, you are generally within the range that the formula considers healthy for your height, sex, and frame size.
Ideal Weight (Midpoint): The single Hamwi estimate before the ±10% spread. It is a statistical reference point, not a personal target — healthy weight varies widely based on muscle mass and body composition.
BMI Range: The body mass index values that correspond to the low and high ends of the weight range. A BMI between roughly 18.5 and 24.9 is generally considered normal weight by the WHO, though BMI does not distinguish between muscle and fat.
Frame Size: Selecting small or large shifts the result by 10%. If you are unsure of your frame, measure wrist circumference — under 6.5 inches for men or under 6 inches for women typically indicates a small frame.
How This Calculator Works
You enter your height (feet and inches or centimeters), sex, and frame size. The tool applies the Hamwi formula — a base weight at 5 feet plus a fixed increment per inch above that, with separate constants for men and women — then scales by ±10% for small or large frames. The result is shown as a weight range and corresponding BMI band. It does not account for age, muscle mass, or body composition.
Quick Questions
Is the Hamwi formula still used in medicine?
Yes, though mainly as a quick reference in dietetics, pharmacy dosing, and nephrology. It was developed in 1964 and remains one of several rule-of-thumb ideal body weight formulas used alongside Devine, Robinson, and Miller.
Why does the result differ from BMI-based ideal weight?
BMI works backward from a target index (usually 21.7–23), while Hamwi uses a fixed per-inch increment. The two approaches come from different populations and assumptions, so they rarely agree exactly, but they generally overlap for average heights.
How do I determine my frame size?
Wrap your thumb and middle finger around your wrist at the narrowest point. If they overlap, you likely have a small frame; if they just touch, medium; if they do not meet, large. Wrist circumference charts from the NIH provide more precise cutoffs.
Should I use this to set a weight loss goal?
Ideal-weight formulas are rough reference points, not clinical targets. A healthcare provider can set a personalized goal that accounts for your body composition, age, medical history, and activity level. Use this number as a starting conversation, not a finish line.