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BMI Calculator

Calculate your body mass index in US or metric units, see which weight category it falls into and find the healthy weight range for your height.

  • Tested formula
  • Instant results
  • Updated September 28, 2026

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BMI formula

BMI = weight (kg) ÷ height (m)²
BMI = 703 × weight (lb) ÷ height (in)²
Example: Someone who is 5 ft 9 in (69 inches) and weighs 160 lb has a BMI of 703 × 160 ÷ 69² = 23.6, which is in the normal range. In metric: 70 kg at 1.75 m gives 70 ÷ 1.75² = 22.9.

BMI categories for adults

BMICategory
Below 18.5Underweight
18.5 – 24.9Normal weight
25.0 – 29.9Overweight
30.0 – 34.9Obesity class I
35.0 – 39.9Obesity class II
40 and aboveObesity 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.

Frequently asked questions

What is a healthy BMI?
For adults, the World Health Organization classifies a BMI of 18.5 to 24.9 as normal weight, 25 to 29.9 as overweight and 30 or more as obese. Below 18.5 is underweight.
Is BMI accurate?
BMI is a quick screening tool, not a diagnosis. It does not distinguish muscle from fat, so muscular athletes may be classed as overweight, and older adults with low muscle mass may have a “normal” BMI despite excess fat. Waist circumference and body fat percentage add useful context.
Is BMI different for men and women?
The adult BMI formula and categories are the same for men and women. Women tend to have more body fat than men at the same BMI, which is one of the limitations of the measure.
Can I use this for children?
No. For people under 20, BMI must be compared with age- and sex-specific growth charts (BMI-for-age percentiles). Ask a pediatrician or use the CDC’s child BMI tool.
Do BMI cut-offs differ for Asian populations?
Yes. Because health risks rise at lower BMI levels in many Asian populations, the WHO suggests that public health action points of 23 (increased risk) and 27.5 (high risk) may be more appropriate for those groups.

Ideal Weight Calculator

Ideal body weight by four clinical formulas.

Body Fat Calculator

Body fat % from tape measurements.

Calorie Calculator

Daily calories to maintain, lose or gain weight.

BMR Calculator

Calories burned at complete rest.

Last reviewed September 28, 2026. Results are estimates for informational purposes; see our disclaimer.