BMI (body mass index) is weight in kilograms divided by height in meters squared, or weight in pounds × 703 divided by height in inches squared. For adults, WHO and CDC categories are under 18.5 underweight, 18.5–24.9 healthy weight, 25–29.9 overweight and 30 or more obesity. BMI is a screening number; it doesn't measure body fat directly.
Key takeaways
- BMI uses only height and weight, so the same formula applies to women and men.
- Adult categories are under 18.5, 18.5–24.9, 25–29.9 and 30 or higher.
- BMI can't tell muscle from fat, so a muscular person can score as overweight without carrying excess fat.
- For a fuller picture, pair BMI with waist size, body fat percentage and a conversation with your doctor.
How does this BMI calculator work?
Enter your height and weight. The calculator returns your BMI to one decimal place, your category, a gauge showing where you sit on the scale, the weight range that gives a healthy BMI at your height and your BMI Prime (BMI divided by 25). If you are outside the healthy range, it shows how much weight change would take you to a BMI of 24.9 or 18.5.
Sex and age don’t enter the adult formula, so the calculator doesn’t ask for them. It also reminds you that BMI does not measure body fat; for that, use the body fat calculator.
What is the BMI formula?
Metric: BMI = weight (kg) ÷ height (m)² Imperial: BMI = 703 × weight (lb) ÷ height (in)²
Both give the same result; 703 is the factor that converts pounds and inches to the metric units.
Worked example
A woman who is 5′5″ (65 inches) and weighs 165 lb: 703 × 165 = 115,995; 65² = 4,225; 115,995 ÷ 4,225 = 27.5. In the CDC’s categories that is overweight (CDC). Her healthy-BMI range at this height is 111–150 lb, so about 15 lb below her current weight is the top of the healthy range.
A man who is 5′10″ and weighs 190 lb has a BMI of 27.3, and a 70 kg adult who is 175 cm tall has a BMI of 22.9.
BMI categories for adults
WHO and the CDC use the same adult cut-offs (WHO; CDC).
| BMI | Category |
|---|---|
| Under 18.5 | Underweight |
| 18.5–24.9 | Healthy weight |
| 25.0–29.9 | Overweight |
| 30.0–34.9 | Obesity, class 1 |
| 35.0–39.9 | Obesity, class 2 |
| 40.0 and over | Obesity, class 3 |
BMI chart by height and weight
Find your height in the left column and read across. Values are computed from the formula above; the last column gives the healthy-weight range (BMI 18.5–24.9) for that height.
| Height | 120 lb | 140 lb | 160 lb | 180 lb | 200 lb | 220 lb | 250 lb | Healthy range |
|---|---|---|---|---|---|---|---|---|
| 5′0″ | 23.4 | 27.3 | 31.2 | 35.2 | 39.1 | 43.0 | 48.8 | 95–127 lb |
| 5′2″ | 21.9 | 25.6 | 29.3 | 32.9 | 36.6 | 40.2 | 45.7 | 101–136 lb |
| 5′4″ | 20.6 | 24.0 | 27.5 | 30.9 | 34.3 | 37.8 | 42.9 | 108–145 lb |
| 5′6″ | 19.4 | 22.6 | 25.8 | 29.1 | 32.3 | 35.5 | 40.4 | 115–154 lb |
| 5′8″ | 18.2 | 21.3 | 24.3 | 27.4 | 30.4 | 33.5 | 38.0 | 122–164 lb |
| 5′10″ | 17.2 | 20.1 | 23.0 | 25.8 | 28.7 | 31.6 | 35.9 | 129–174 lb |
| 6′0″ | 16.3 | 19.0 | 21.7 | 24.4 | 27.1 | 29.8 | 33.9 | 136–184 lb |
| 6′2″ | 15.4 | 18.0 | 20.5 | 23.1 | 25.7 | 28.2 | 32.1 | 144–194 lb |
BMI calculator for women and men
The formula and cut-offs are identical for women and men. What differs is body composition: at the same BMI, women typically carry more body fat than men. That is the reason a body fat estimate adds information, and why the ideal weight calculator uses different constants for each sex.
What are the limits of BMI?
BMI is a screening tool. The CDC describes it as a way to screen for weight categories that may lead to health problems, not as a diagnostic of body fatness or health (CDC). WHO calls it a rough guide, noting that it may not correspond to the same degree of fatness in different individuals (WHO).
- Muscle. Muscle weighs more than fat per unit volume, so athletes and lifters can score high. The example man above has a BMI of 27.3, yet a Navy-method body fat of 16.5% (see the body fat calculator).
- Age. BMI doesn’t account for the loss of muscle with age, so an older adult can have a “healthy” BMI and still carry more fat than expected.
- Population differences. Some health bodies use adjusted cut-offs for certain groups. Ask your doctor how BMI applies to you.
- Fat distribution. BMI doesn’t show where fat is carried, and waist size adds information.
What should I do with my BMI?
Treat it as a starting point. If you want to change your weight, estimate your calories with the TDEE calculator, then use the calorie deficit calculator or weight loss calculator to set a pace. Talk to a doctor or registered dietitian if your BMI is under 18.5 or above 30, if you are pregnant, or if you have a history of disordered eating.
Frequently asked questions
What is the BMI formula?
In metric units, BMI = weight (kg) ÷ height (m)². In US units, BMI = 703 × weight (lb) ÷ height (in)². For example, a 5′5″ (65 in) adult weighing 165 lb has a BMI of 703 × 165 ÷ 65², which is 27.5.
What is a healthy BMI?
For adults, 18.5 to 24.9 is classed as a healthy weight by the CDC and WHO. At 5′5″ that is roughly 111–150 lb (50–68 kg). Healthy for you also depends on muscle, age, health conditions and where you carry fat, so discuss it with your doctor.
Is the BMI calculator different for women and men?
No. The adult BMI formula and categories are the same for both. Women and men with the same BMI tend to have different body fat percentages, though, which is one reason to check body fat as well.
Why is BMI criticized?
BMI uses only height and weight, so it can't tell muscle from fat or show where fat is stored. WHO describes it as a rough guide because it may not correspond to the same degree of fatness in different individuals. It is best treated as a screening tool, not a diagnosis.
Does BMI work for athletes?
Often not. A lifter with lots of muscle can have a BMI above 25 with a low body fat percentage. Use body fat, waist size and performance to judge your composition instead.
Can I use BMI for children?
No. This calculator is for adults aged 18 and over. Children and teens are assessed with age- and sex-specific growth charts, so ask a pediatrician.
References
- World Health Organization (2024). Obesity and overweight — fact sheet. World Health Organization.
- Centers for Disease Control and Prevention (2024). Adult BMI Calculator and categories. U.S. Centers for Disease Control and Prevention.