There’s no single number that qualifies as your ideal weight. The answer depends on your height, sex, age, body composition, and ethnic background. BMI gives you a starting range, but newer metrics like waist-to-height ratio and body fat percentage paint a more accurate picture of whether your weight is healthy.
BMI: The Standard Starting Point
Body mass index is calculated by dividing your weight in kilograms by your height in meters squared. The CDC uses these categories for adults 20 and older:
- Underweight: below 18.5
- Healthy weight: 18.5 to 24.9
- Overweight: 25 to 29.9
- Obesity: 30 or higher
For a person who is 5’9″, that healthy range translates to roughly 125 to 169 pounds. That’s a 44-pound spread, which tells you something important: “ideal” isn’t a single number. It’s a zone, and where you fall within it depends on factors BMI doesn’t capture.
What the Classic Formulas Calculate
Doctors and pharmacists have long used height-based formulas to estimate ideal body weight. The most common ones work like this: start with a base weight for someone who is 5 feet tall, then add a fixed amount per inch above that. The Hamwi formula, for example, sets the base at 106 pounds for men and 100 pounds for women, adding 6 pounds per inch for men and 5 for women. The Devine formula uses similar logic but produces slightly different numbers.
Here’s what those formulas yield for a few common heights:
- 5’4″ woman: about 120 lbs (Hamwi) or 121 lbs (Devine)
- 5’9″ man: about 160 lbs (Hamwi) or 155 lbs (Devine)
- 5’6″ woman: about 130 lbs (Hamwi) or 131 lbs (Devine)
- 6’0″ man: about 178 lbs (Hamwi) or 177 lbs (Devine)
These formulas were designed for quick clinical estimates, not personal health goals. They don’t account for muscle mass, bone density, or ethnic differences. Treat them as rough reference points rather than targets.
Why BMI Misses the Full Picture
BMI can’t distinguish between muscle and fat. A bodybuilder with 6% body fat can register a BMI above 30, placing them in the “obese” category despite being exceptionally lean. Research on elite military personnel found that BMI couldn’t differentiate between highly trained soldiers and untrained individuals of the same height and weight. The trained group classified as “overweight” by BMI actually had less body fat than the untrained group classified as “normal.”
The reverse problem is equally concerning. BMI underestimates body fat in people with low muscle mass, particularly older adults and those with chronic illness. You can have a “healthy” BMI while carrying a disproportionate amount of fat around your organs.
Body Fat Percentage Tells You More
Body fat percentage measures what portion of your total weight comes from fat tissue. Because men and women carry fat differently, the ranges are sex-specific:
- Athletes: 6 to 13% for men, 12 to 19% for women
- General fitness: 14 to 17% for men, 20 to 24% for women
- Average/acceptable: 18 to 24% for men, 25 to 29% for women
Most people aiming for general health land in the fitness or average categories. You don’t need athlete-level body fat to be healthy. Getting an accurate body fat reading typically requires tools beyond a bathroom scale, such as skinfold calipers, bioelectrical impedance devices, or a DEXA scan through your doctor.
Where You Carry Fat Matters
Two people at the same weight can have very different health risks depending on where their fat sits. Fat stored deep around organs in the abdomen, called visceral fat, is metabolically active. It responds to hormones and influences how your body processes sugar and cholesterol. High levels of visceral fat raise the risk of heart disease, diabetes, and circulatory problems like atherosclerosis. Fat stored just under the skin on hips and thighs carries far less metabolic risk.
You can’t see or feel visceral fat directly, but your body measurements give you a reliable estimate. Two simple checks are worth knowing.
Waist-to-Height Ratio
Measure your waist at the narrowest point (usually at your navel) and divide by your height. If the result is 0.5 or higher, you’re carrying excess central fat. This cutoff works across sexes, age groups, and ethnic backgrounds, making it one of the most practical self-checks available. Research and meta-analyses have found this ratio is equal to or slightly better than waist circumference alone, and superior to BMI, for predicting heart and metabolic problems. The simplest version: keep your waist measurement to less than half your height.
Waist-to-Hip Ratio
Divide your waist circumference by the widest part of your hips. Risk begins climbing above 0.78 for women and 0.87 for men, though these thresholds may vary somewhat by population. If your number exceeds those cutoffs, your fat distribution pattern leans toward abdominal storage, which warrants attention regardless of what the scale says.
Adjustments for Age
The “ideal” BMI shifts upward as you get older. A systematic review of mortality studies in people over 65 found that the lowest death rates were associated with a BMI between 25 and 30, a range that would be classified as “overweight” by standard categories. For women over 65, some studies pinpointed the sweet spot around 27 to 30. In adults aged 71 to 93, the lowest mortality range extended from about 24 all the way up to 39.
The likely explanation is that carrying modest extra weight in older age provides reserves during illness, surgery, or periods of reduced appetite. Older adults who are too lean face higher risks from falls, infections, and muscle loss. If you’re over 65, a BMI in the mid-to-upper 20s is generally a better target than striving for 22.
Adjustments for Ethnicity
Standard BMI cutoffs were developed primarily from data on European populations. For people of Asian descent, health risks begin at lower weights. A WHO expert panel reviewed data from multiple Asian countries and recommended lowering the overweight threshold to a BMI of 23 (instead of 25) and the obesity threshold to 27.5 (instead of 30). At the same BMI, Asian populations tend to carry more body fat and face higher metabolic risk than white populations. If you’re of Asian descent, the standard “healthy weight” range may overestimate how much weight is safe for you.
How to Find Your Own Target
Rather than fixating on one number, use multiple measurements together. Start with BMI for a ballpark range, then check your waist-to-height ratio with a tape measure. If you have access to body fat testing, that adds another useful layer. No single metric captures everything, but combining two or three gives you a reliable picture.
Your ideal weight is also the weight where you function well: sleeping soundly, moving without joint pain, maintaining stable energy, and keeping blood sugar and blood pressure in normal ranges. A number that checks every box on a chart but leaves you constantly hungry or unable to sustain your activity level isn’t truly ideal for you. The most useful target is one you can maintain through habits you’re willing to keep for years, not weeks.