BMI Calculator

BMI formula

BMI = weight (kg) ÷ height (m)² BMI = 703 × weight (lb) ÷ height (in)²

Worked example

Someone who is 5 ft 9 in (69 in) and weighs 170 lb has a BMI of 703 × 170 ÷ 69² = 703 × 170 ÷ 4,761 = 25.1, which is just inside the overweight range.

BMI categories for adults

BMI	Category
Below 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 and above	Obesity class 3

These are the standard categories used by the World Health Organization and the US Centers for Disease Control and Prevention for adults.

Limits of BMI

• BMI does not measure body fat directly. Muscular people can have a high BMI without excess fat.
• It does not show where fat is stored. Waist size adds useful information.
• Healthy ranges can differ by ethnicity; some guidelines use lower cut-offs for people of Asian descent.
• It is not designed for children, pregnant women or the very elderly.

BMI is a screening tool, not a diagnosis. Talk to a doctor or registered dietitian about your weight and health.

Frequently asked questions

What is a healthy BMI?

For most adults, a BMI from 18.5 to 24.9 is considered a healthy weight range.

How do I calculate BMI in pounds and inches?

Multiply your weight in pounds by 703, then divide by your height in inches squared.

Is BMI accurate for athletes?

Not always. Muscle weighs more than fat for its size, so very muscular people may be classed as overweight even with low body fat.

Can children use this BMI calculator?

No. For ages 2 to 19, BMI must be compared with growth charts for age and sex, which this adult calculator does not do.

What is BMI Prime?

It is your BMI divided by 25, the upper limit of the healthy range. A value below 1.0 means you are under that limit.