Ideal body weight (IBW) is calculated using your height and sex, not your actual weight. The most common method, the Devine formula, starts with a base weight at 5 feet tall and adds a fixed amount for each additional inch. For men: 50 kg + 2.3 kg per inch over 5 feet. For women: 45.5 kg + 2.3 kg per inch over 5 feet. So a 5’6″ woman would have an IBW of about 58.5 kg (129 lbs), and a 5’10” man would come out to 73 kg (161 lbs).
The Four Main Formulas
Several formulas have been developed since the 1960s, and they all work the same basic way: start with a base weight for someone who is 5 feet tall, then add a set number of pounds or kilograms for each inch above that. They differ in those starting values and increments, which means they can give you noticeably different results for the same person.
Hamwi (1964)
- Men: 106 lbs for 5 feet, plus 6 lbs per inch over 5 feet
- Women: 100 lbs for 5 feet, plus 5 lbs per inch over 5 feet
Devine (1974)
- Men: 50 kg for 5 feet, plus 2.3 kg per inch over 5 feet
- Women: 45.5 kg for 5 feet, plus 2.3 kg per inch over 5 feet
Robinson (1983)
- Men: 52 kg for 5 feet, plus 1.9 kg per inch over 5 feet
- Women: 49 kg for 5 feet, plus 1.7 kg per inch over 5 feet
Miller (1983)
- Men: 56.2 kg for 5 feet, plus 1.41 kg per inch over 5 feet
- Women: 53.1 kg for 5 feet, plus 1.36 kg per inch over 5 feet
The Devine formula is the most widely used in clinical settings and the one you’ll see in most online calculators. The Hamwi method is popular in nutrition practice because it works in pounds and is easy to do in your head. Miller tends to produce slightly higher estimates, especially for shorter people, because of its higher base weight.
A Worked Example
Take a woman who is 5’4″ (64 inches). That’s 4 inches over 5 feet. Using the Devine formula: 45.5 + (2.3 × 4) = 54.7 kg, or about 120.5 lbs. Using the Hamwi formula: 100 + (5 × 4) = 120 lbs. Those two happen to land close together, but for a taller person the gap between formulas widens.
For a man who is 6’0″ (72 inches), that’s 12 inches over 5 feet. Devine gives 50 + (2.3 × 12) = 77.6 kg (171 lbs). Hamwi gives 106 + (6 × 12) = 178 lbs. Miller gives 56.2 + (1.41 × 12) = 73.1 kg (161 lbs). A spread of 17 pounds across three formulas for the same person highlights that none of these are precise targets.
Adjusting for Body Frame Size
One reason these formulas produce a range rather than a single “correct” number is that people of the same height can have very different skeletal builds. A common adjustment uses wrist circumference to classify you as small, medium, or large framed. You measure around the narrowest part of your wrist, just below the wrist bone, with a flexible tape.
For women 5’2″ to 5’5″, a wrist under 6 inches indicates a small frame, 6 to 6.25 inches is medium, and over 6.25 inches is large. For men over 5’5″, a wrist of 5.5 to 6.5 inches is small, 6.5 to 7.5 inches is medium, and over 7.5 inches is large. The general rule: subtract about 10% from your IBW for a small frame, keep it as-is for a medium frame, and add about 10% for a large frame.
Getting Your Height Right
Because every formula multiplies your height above 5 feet, even a small error in measurement compounds the result. An inch off means 5 to 6 pounds off in the Hamwi formula. If you’re measuring at home, stand against a flat wall on an uncarpeted floor without shoes. Your heels, buttocks, shoulder blades, and the back of your head should touch the wall. Have someone place a flat ruler on top of your head, mark where the bottom of the ruler meets the wall, then measure from the floor to that mark with a tape measure. Take the measurement at least twice.
Why These Formulas Have Limits
All four formulas use only two inputs: height and sex. They ignore muscle mass, bone density, age, and ethnicity. A 5’10” man with a sedentary desk job and a 5’10” competitive rower get the same IBW, even though the rower may carry 20 or more extra pounds of muscle and be in excellent health. The formulas were also developed primarily from insurance company data on white American and European populations, so they may not reflect healthy weight ranges for people of other backgrounds.
These formulas also break down at the extremes of height. For very short adults (under 5 feet), the base values may overestimate healthy weight; for very tall adults, the linear per-inch additions can underestimate it. None of the formulas account for age-related changes in body composition either. Adults naturally gain some body fat and lose some muscle as they age, even at a stable weight.
Where IBW Is Actually Used
You might assume IBW is mainly a personal health tool, but its biggest use is in hospitals. Ventilator settings for patients with lung injury are calculated at 6 to 8 milliliters of air per kilogram of IBW, not actual weight, because lung size tracks with height rather than how much someone weighs. Certain medications are also dosed based on IBW for the same reason: organ size and drug distribution don’t scale with excess body fat the way they scale with height.
IBW for Children
The adult formulas don’t apply to children. Pediatric IBW is typically calculated using growth charts rather than a single equation. The most common approach plots a child’s height on a growth chart, finds where that height falls on the 50th percentile for age, and reads the corresponding weight at that same percentile. For children taller than 5 feet, a modified formula (the Traub method) can be used: for boys, 39 + (2.27 × inches over 60); for girls, 42 + (2.27 × inches over 60), both in kilograms.
Better Ways to Assess Healthy Weight
If your goal is understanding your personal health risk rather than hitting a specific number on the scale, there are more informative measures than IBW.
Waist-to-height ratio is one of the simplest. Measure your waist at the navel, then divide by your height (both in the same unit). A ratio under 0.5 is the universal target for both men and women, across ethnicities and age groups. The message is straightforward: keep your waist circumference to less than half your height. A prospective study found that people aged 12 to 39 with a ratio above 0.65 had a 139% greater risk of dying before age 55 compared to those below 0.53. Unlike IBW formulas, waist-to-height ratio captures where you carry fat, which matters more for heart disease and metabolic health than total weight alone.
Body fat percentage provides even more detail. Healthy ranges for adults aged 21 to 39 are roughly 8 to 20% for men and 21 to 32% for women. You can estimate body fat with a simple tape measure using the Navy method (neck and waist for men; neck, waist, and hips for women), or more precisely with tools like a DEXA scan. Body fat percentage distinguishes between someone who is heavy because of muscle and someone who is heavy because of excess fat, a distinction no height-based formula can make.
IBW formulas give you a quick reference point, and they remain essential in clinical dosing and ventilator management. But for personal health, they work best as a rough starting range rather than a goal weight. Combining your IBW estimate with a waist-to-height check and, if possible, a body fat measurement gives you a far more complete picture of where you stand.