Ideal body weight (IBW) is calculated using height-based formulas that estimate a target weight for a given height, separated by sex. The most widely used is the Devine formula: for men, start at 110 pounds for 5 feet tall and add 5.1 pounds per inch above that; for women, start at 100 pounds for 5 feet and add 5.1 pounds per inch. These formulas give a single number, not a range, and they don’t account for body composition, frame size, or age, so they work best as a quick starting point rather than a definitive answer.
The Four Main IBW Formulas
Four formulas are commonly referenced in clinical and nutrition settings. All follow the same structure: a base weight at 5 feet (60 inches) of height, plus a fixed amount for each additional inch. The formulas differ in their base weights and per-inch increments, which means they can produce noticeably different results for the same person.
Devine Formula (1974)
This is the default in most medical settings. Men: 50 kg + 2.3 kg for each inch over 5 feet. Women: 45.5 kg + 2.3 kg for each inch over 5 feet. In pounds, that translates to a base of about 110 lb for men and 100 lb for women, adding roughly 5.1 lb per inch. A 5’10” man gets an IBW of about 166 lb. A 5’6″ woman gets about 130 lb.
Hamwi Formula (1964)
Men: 48 kg + 2.7 kg per inch over 5 feet. Women: 45.5 kg + 2.2 kg per inch over 5 feet. The Hamwi formula adds slightly more weight per inch for men, so taller men will see a higher estimate here than with Devine. For a 5’10” man, Hamwi gives about 173 lb compared to Devine’s 166 lb.
Robinson Formula (1983)
Men: 52 kg + 1.9 kg per inch over 5 feet. Women: 49 kg + 1.7 kg per inch over 5 feet. Robinson uses a higher starting weight but a smaller increment, so it produces more moderate estimates for taller individuals and higher estimates for shorter ones.
Miller Formula (1983)
Men: 56.2 kg + 1.41 kg per inch over 5 feet. Women: 53.1 kg + 1.36 kg per inch over 5 feet. Miller starts with the highest base weight and the smallest per-inch addition. This formula tends to give the highest results for people around 5 feet tall and the lowest for very tall people.
To see the practical spread: for a 5’4″ woman, the four formulas produce estimates ranging from roughly 120 lb (Devine) to 126 lb (Miller). For a 6’2″ man, the range is about 176 lb (Devine) to 185 lb (Robinson). No single formula is objectively “correct.” If you want one number, Devine is the standard. If you want a more realistic picture, look at the range all four produce and treat that as your ballpark.
A Worked Example
Say you’re a woman who is 5’5″ (65 inches). Using the Devine formula: start with 45.5 kg, then add 2.3 kg for each of the 5 inches above 60. That’s 45.5 + (2.3 × 5) = 45.5 + 11.5 = 57 kg, or about 126 lb. To convert kilograms to pounds, multiply by 2.205.
For a man at 5’11” (71 inches): 50 + (2.3 × 11) = 50 + 25.3 = 75.3 kg, or about 166 lb. If your height is exactly 5 feet, the base number alone is your IBW. If you’re shorter than 5 feet, these formulas don’t apply, and BMI-based methods or growth chart approaches are more appropriate.
How IBW Differs From BMI
BMI and IBW answer different questions. BMI takes your actual weight and height and produces a ratio. The World Health Organization classifies a BMI under 18.5 as underweight, 18.5 to 24.9 as normal weight, 25 and above as overweight, and 30 and above as obese. IBW, by contrast, ignores your current weight entirely. It tells you what someone of your height and sex “should” weigh according to population averages.
You can use both together. Calculate your IBW to get a reference point, then check your BMI to see where your current weight falls relative to the healthy range. A BMI of 18.5 to 24.9 corresponds to a fairly wide weight window for any given height. For a 5’6″ person, that’s roughly 115 to 155 lb. The IBW formula gives you a single point within that window, typically near the middle.
Why These Formulas Exist
IBW formulas were originally developed for practical medical purposes, not as personal fitness goals. The Devine formula was created in 1974 specifically for calculating medication doses. Many drugs distribute differently in fat tissue versus lean tissue, so clinicians need a way to estimate lean body mass quickly. Medications for sedation, pain management, and blood pressure support in hospital settings are still frequently dosed using IBW rather than a patient’s actual weight, especially in people with obesity.
When someone weighs more than 30% above their calculated IBW, clinicians often switch to a modified calculation called adjusted body weight: IBW + 0.4 × (actual weight minus IBW). This splits the difference, acknowledging that some extra tissue does contribute to how the body processes a drug, but not proportionally.
IBW for Children and Teens
The adult formulas don’t work for anyone under 18. Children are still growing, so their ideal weight depends on age, height, and developmental stage. The most common pediatric approach is the McLaren method, which uses CDC growth charts. You plot a child’s height on the chart, find where it crosses the 50th percentile line for height, then read across to find the corresponding 50th percentile weight. That weight is the child’s IBW.
For children and adolescents who are at least 5 feet tall, the Traub formula works like the adult versions: for boys, 39 kg + 2.27 kg per inch over 5 feet; for girls, 42.2 kg + 2.27 kg per inch over 5 feet. For children under 5 feet, Traub uses a height-squared calculation: height in centimeters, squared, multiplied by 1.65, then divided by 1,000, giving the result in kilograms.
Why IBW Shifts for Older Adults
For people over 65, the standard “healthy” weight ranges may be too low. A large meta-analysis covering nearly 198,000 older adults with an average follow-up of 12 years found that mortality risk was lowest at a BMI of 23 to 24, which is the upper end of what’s classified as normal weight. Being at the lower end of the normal range actually carried measurable risk: a BMI of 21 to 21.9 was associated with 12% higher mortality, and a BMI of 20 to 20.9 with 19% higher mortality. Risk didn’t begin climbing on the high side until a BMI above 33.
In practical terms, this means an older adult whose IBW calculation points to a BMI of 20 or 21 may actually be healthier carrying a few extra pounds. The standard IBW formulas don’t adjust for age, so if you’re over 65, it’s worth knowing that the formulas may point you toward a weight that’s lighter than what the mortality data supports.
Where IBW Formulas Fall Short
Every IBW formula shares the same blind spots. They use only two inputs, height and sex, and ignore everything else about your body. Someone with a large skeletal frame will naturally weigh more than someone with a small frame at the same height, and none of the formulas capture this. The Metropolitan Life Insurance Company addressed this decades ago by publishing weight tables with separate columns for small, medium, and large frames. For a 5’8″ man, their ranges span from 140 lb (small frame) to 172 lb (large frame), a 32-pound spread that a single IBW number can’t reflect.
Athletes and anyone who carries significant muscle mass will consistently overshoot their IBW. Muscle is denser than fat, so a lean, muscular person at 180 lb and a sedentary person at 180 lb have very different health profiles despite identical IBW comparisons. The formulas also don’t account for ethnicity, bone density, or where you carry your weight, all of which affect health risk.
Other Ways to Assess Healthy Weight
If you want a more complete picture than a single number, the waist-to-height ratio is one of the simplest and most informative alternatives. Measure your waist at your navel, then divide by your height (both in the same unit). A ratio below 0.5 falls in the healthy range. Between 0.5 and 0.59 indicates increased risk of heart disease and metabolic problems. At 0.6 or above, the risk is highest. This measurement captures abdominal fat specifically, which is more strongly linked to cardiovascular and metabolic disease than overall weight.
You can also use BMI as a range rather than relying on a single IBW number. Multiply your height in meters squared by 18.5 and then by 24.9 to find the low and high ends of the normal-weight range. This gives you a window of 30 to 40 pounds for most heights, which is more realistic than a single target. Combining a healthy BMI range with a waist-to-height ratio under 0.5 gives you a practical, two-part check that accounts for both overall weight and fat distribution.