BMI formula
BMI = 703 × weight (lb) ÷ height (in)²
BMI categories for adults
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal weight |
| 25.0 – 29.9 | Overweight |
| 30.0 – 34.9 | Obesity class I |
| 35.0 – 39.9 | Obesity class II |
| 40 and above | Obesity class III |
What your BMI does and doesn’t tell you
Large population studies link a higher BMI with greater risk of type 2 diabetes, high blood pressure, heart disease and some cancers, and a very low BMI with nutritional deficiencies and bone loss. That makes it a useful first check. But two people with the same BMI can have very different body composition. If your result surprises you, look at your waist size (over 40 in / 102 cm for men or 35 in / 88 cm for women signals higher risk) or estimate body fat with our body fat calculator.
BMI Prime, shown in the result, is your BMI divided by 25 — the upper limit of normal. A value of 1.00 is exactly at the limit; 1.20 means 20% above it.
This calculator is for adults aged 20 and older and is not a substitute for advice from a healthcare professional.
How to use the calculator
- Choose U.S. (feet, inches, pounds) or metric (centimeters, kilograms) units.
- Enter your height and weight. Weigh yourself in the morning, without shoes, for the most consistent result.
- Read your BMI, its category and the healthy weight range for your height.
BMI weight ranges by height
| Height | Healthy weight (BMI 18.5–24.9) | Overweight (25–29.9) | Obese (30+) |
|---|---|---|---|
| 5′0″ | 95–128 lb | 128–153 lb | 154 lb+ |
| 5′3″ | 104–141 lb | 141–169 lb | 169 lb+ |
| 5′6″ | 115–154 lb | 155–185 lb | 186 lb+ |
| 5′9″ | 125–169 lb | 169–202 lb | 203 lb+ |
| 6′0″ | 136–184 lb | 184–220 lb | 221 lb+ |
| 6′3″ | 148–199 lb | 200–239 lb | 240 lb+ |
BMI for children and teens
For ages 2 to 19, BMI is interpreted with age- and sex-specific percentiles rather than fixed cut-offs, because body fat changes as children grow. The CDC classes a BMI at or above the 85th percentile as overweight and at or above the 95th as obesity. This calculator uses adult categories, so for children use a pediatric BMI-for-age chart or ask a pediatrician.
Different cut-offs for some groups
Research shows that people of Asian descent tend to have more body fat and higher risk of type 2 diabetes at the same BMI. The World Health Organization and several national guidelines therefore suggest lower action points for Asian populations — for example, treating a BMI of 23 or more as increased risk and 27.5 or more as high risk. Older adults may have the lowest mortality risk at a slightly higher BMI, around 25–27, because some reserve is protective in older age.
Beyond BMI
BMI is a quick screening tool, not a measure of body fat or health. It can classify muscular athletes as overweight and miss excess fat in people with little muscle. For a fuller picture, combine it with:
- Waist measurement or the waist-to-height ratio to assess belly fat.
- Body fat percentage from the body fat calculator.
- Blood pressure, blood sugar and cholesterol measured by a health professional.
- Fitness and habits: activity, diet quality, sleep and smoking affect health at every BMI.
Sources
- World Health Organization. Body mass index (BMI) classification for adults.
- Centers for Disease Control and Prevention (CDC). About Adult BMI; Child and Teen BMI.
- WHO Expert Consultation. Appropriate body-mass index for Asian populations. The Lancet, 2004.