What is BMI?
Body mass index (BMI) is a number worked out from your height and weight. Doctors use it as a quick screening tool to see whether a person’s weight is likely to be healthy for their height.
How to use this calculator
- Choose your units. Pick US (feet, inches, pounds) or metric (centimeters, kilograms).
- Enter your height and weight. Weigh yourself in the morning, without shoes.
- Read your result. Your BMI, its category and your healthy weight range update instantly.
BMI formula
US units: BMI = 703 × weight (lb) ÷ height (in)²
Metric units: BMI = weight (kg) ÷ height (m)²
Worked example
Sarah is 5 ft 7 in (67 inches) tall and weighs 165 lb. 67 × 67 = 4,489. 165 ÷ 4,489 = 0.03676. 0.03676 × 703 = 25.8, which is in the overweight range. For her height, a healthy weight is about 118 to 159 lb.
BMI chart for adults
| BMI | Category | Weight at 5′7″ |
|---|---|---|
| Below 18.5 | Underweight | Under 118 lb |
| 18.5 – 24.9 | Healthy weight | 118 – 159 lb |
| 25 – 29.9 | Overweight | 160 – 191 lb |
| 30 and above | Obesity | 192 lb or more |
What BMI doesn’t tell you
BMI can’t tell muscle from fat, and it doesn’t show where fat is stored. People under 20 need a BMI-for-age percentile, and BMI isn’t used to assess weight during pregnancy.
Frequently asked questions
What is a healthy BMI for adults?
For most adults aged 20 and over, a BMI from 18.5 to 24.9 is in the healthy weight range.
Is BMI accurate for athletes?
Not always. BMI can’t tell muscle from fat, so very muscular people can have a high BMI without excess body fat.
Can I use this calculator for children or teens?
No. People under 20 should use a BMI-for-age percentile chart, because healthy BMI changes with age and sex.
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