BMI calculator (body mass index)

Calculate your BMI in a few seconds

Body mass index (BMI) compares your weight with your height. It is the measure the World Health Organization (WHO) and doctors use as a first look at an adult's weight for their height. This BMI calculator gives your result to one decimal place, the matching category spelled out in words, a colour gauge with a marker, and the weight range that matches a BMI of 18.5 to 24.9 at your height.

It works in pounds, feet and inches by default, and switches to kilograms and centimetres in one click.

How to use it

1. Under "Units", keep "Imperial (lb, ft, in)" or pick "Metric (kg, cm)".
2. Enter "Weight (lb)", then your height in "Height: feet (ft)" "and inches (in)". For 5 ft 9 in, type 5 and 9.
3. The result appears straight away under "Your BMI", with the category, the weight range and the working. The marker moves along the gauge and the matching row of the table is highlighted.
4. If you like, tick "Add waist size (optional)" to get your waist-to-height ratio.

Values outside the expected range, such as 59 in the feet box, are flagged in red.

The BMI formula, with a worked example

In metric units, BMI = weight (kg) ÷ height (m)². In pounds and inches, the usual shortcut is BMI = 703 × weight (lb) ÷ height (in)². The calculator converts pounds and inches exactly (1 lb = 0.45359237 kg, 1 in = 2.54 cm).

Example: someone who weighs 154 lb and is 5 ft 9 in tall. 5 ft 9 in is 69 inches, and 69 × 69 = 4,761. So 703 × 154 ÷ 4,761 = 22.74, rounded to 22.7, which falls in the healthy weight range. At 5 ft 9 in, a BMI of 18.5 to 24.9 matches a weight of 126 to 168 lb. Both ends are rounded inwards to stay within the range.

WHO BMI categories for adults

The category is based on the BMI rounded to one decimal, the figure you see on screen. On its own, it does not say whether someone is healthy.

What BMI does not tell you

• Muscle: BMI cannot tell muscle from fat. A muscular athlete or rugby player may have a high BMI without carrying extra fat.
• Age: muscle mass tends to fall with age, so in older adults a BMI in the normal range can hide a loss of muscle.
• Where fat is carried: at the same BMI, fat around the waist does not mean the same as fat on the hips.
• Ethnic background: the link between BMI and health varies between populations.

The adult categories do not apply during pregnancy.

Children and teenagers: growth charts

Under 18, body shape changes as children grow. BMI is worked out the same way but read on BMI-for-age growth charts, by age and sex, usually as a percentile. This calculator does not do that: for a child or teenager, ask your doctor, pediatrician or school nurse.

Waist size as a second measure

Waist size gives an idea of fat around the middle, which BMI cannot show. The waist-to-height ratio divides one by the other, in the same unit. A 32 in waist at 5 ft 9 in (69 in) gives 32 ÷ 69 = 0.46. A mark of 0.5 is often quoted; treat it as something to discuss with a doctor, not a verdict.

Frequently asked questions

What is a healthy BMI?

For adults, the WHO puts a BMI of 18.5 to 24.9 in the healthy range. Your doctor will look at it alongside the rest of your health.

How do I calculate BMI by hand in pounds?

Turn your height into inches, multiply it by itself, divide your weight in pounds by that number, then multiply by 703. For 200 lb at 6 ft (72 in): 703 × 200 ÷ 5,184 = 27.1.

Can I use it for my child?

No. The number itself would be right, but adult categories do not apply under 18. Children's BMI is read on growth charts with a health professional.

Is my data sent anywhere?

No. It runs in your browser, which keeps your last entry until you press "Clear all".