About BMI Calculator
Body mass index compares your weight with your height, giving one number that doctors and researchers use as a first check on weight-related health risk. Enter your height and weight in metric or imperial units, and you see the number, the category it falls in, and what the healthy range works out to at your height.
BMI is a screening measure, and it does not diagnose anything. It cannot tell muscle from fat, and it says nothing about where fat is carried, your blood pressure, your blood tests or how you feel. Two people with the same BMI can have very different health. Treat the number as a prompt for a conversation with a doctor, particularly if it surprises you.
How it works
The formula is weight in kilograms divided by height in meters squared. At 175 cm and 70 kg, that is 70 divided by 1.75 times 1.75, or 22.9. Imperial values are first converted exactly, with 1 lb as 0.45359237 kg and 1 inch as 2.54 cm. The result is then placed in the World Health Organization's adult categories, which are shown in the table on the page.
The categories are: under 18.5 is underweight, 18.5 to 24.9 is healthy weight, 25 to 29.9 is pre-obesity (overweight), 30 to 34.9 is obesity class I, 35 to 39.9 is class II, and 40 and over is class III. The healthy range line runs the formula backward, multiplying 18.5 and 25 by your height squared. Heights outside 100 to 250 cm and weights outside 25 to 400 kg get a message asking you to check the entry, which catches values typed in the wrong units.
How to use BMI Calculator
- Under Units, choose Metric or Imperial.
- Enter your height and weight, or press Try an example.
- Read your BMI, the category and the healthy range for your height.
- Read the note under the table about who this number does and does not suit.
Two real runs
175 cm, 70 kg
180 cm, 92 kg22.9, Healthy weight
At this height, the WHO healthy range of BMI 18.5 to 24.9 works out to about 56.7 kg to 76.6 kg.
28.4, Pre-obesity (overweight)
At this height, the WHO healthy range of BMI 18.5 to 24.9 works out to about 59.9 kg to 81.0 kg.A muscular person at 180 cm and 92 kg could get the second result and be in excellent shape. The number describes size, not fitness or fat.
When it helps
- A quick check before a check-up, so you have a number to ask about
- Seeing the weight range that matches a healthy BMI at your height
- Converting height and weight between units for a health form that asks for BMI
- Following a long-term trend, alongside measures such as waist size and your doctor's advice
Tips for a better result
- Use a recent measured height and weight. People tend to overstate height, and small errors in height shift the result more than you would expect, because height is squared.
- Look at the trend over time and not a single reading. Weight can move by a kilogram or more in a day with water and food.
- Waist measurement adds what BMI misses, since fat around the middle carries more risk. A doctor may check both.
- If your number worries you, talk to a doctor before making big changes. Crash diets can do more harm than a moderately high BMI.
Good to know
- It is not medical advice and cannot tell you whether you are healthy.
- It suits adults only. Children and teenagers are assessed with age and sex growth charts, and this page does not cover them.
- It does not apply in pregnancy.
- It can read high for muscular people and low for older adults who have lost muscle, as it cannot measure body fat.
- Health risk at the same BMI differs between ethnic groups, and some countries use lower cut-offs for Asian populations. This tool uses the WHO's general adult categories only.
Questions people ask
Is BMI an accurate measure of health?
It is a rough population-level screen. It correlates with health risk across large groups, but it can misjudge individuals, because it does not separate fat from muscle or show where fat is carried. It cannot tell you that you are or are not healthy.
What is a healthy BMI?
Under the WHO's adult categories, 18.5 to 24.9 is the healthy weight range. This does not mean everyone inside it is healthy, or that everyone outside it is unhealthy.
How do I calculate BMI in pounds and inches?
Multiply your weight in pounds by 703 and divide by your height in inches squared. This page converts to metric exactly instead, and 5 ft 9 in with 160 lb comes out at 23.6.
Is my information stored?
No. The sum runs in your browser, and height and weight are not sent anywhere or saved.
What to use next
- Weight Converter: to convert between kilograms, pounds and stone
- Length Converter: to turn a height into the units a form asks for
- Age Calculator: if a form also wants your exact age
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