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BMI Calculator

Use this metric and imperial BMI calculator tool to work out your body mass index and get an indication of whether your weight might be affecting your health. This BMI tool is intended for use by men and women of 18 years and over.

Disclaimer: The results given by this bmi calculator should be used only as a guide and should not replace medical advice. Please bear in mind that, when interpreting the results of this body mass index calculator, other factors such as muscle structure and ethnic origin should be considered. For example, a person with a lot of muscle might have a higher BMI, when their body is actually perfectly healthy, due to the fact that muscle weighs more than fat. Always speak to a Doctor or health professional for advice before making any dramatic changes to your lifestyle.

BMI calculations

Body Mass Index is calculated using either the metric or imperial BMI formula. In both cases, you divide your weight by your height raised to the power of 2. With the imperial BMI formula, you then multiply the resulting figure by 703.

If you wish to calculate your BMI manually rather than using the BMI calculator, I've included some simple instructions and formulae below. It's important that if you use these, you ensure that your units are in the same unit system (metric or imperial) and the correct corresponding unit.

If you need to convert between units of weight, use our kilos and pounds converter.

To calculate your BMI

  1. Divide your weight (lb) by your height (in).
    Example: 154lb ÷ 71in = 2.169
  2. Divide your answer from part 1 by your height again.
    Example: 2.169 ÷ 71 = 0.03055
  3. Multiply your answer from part 2 by 703.
    Example: 0.03055 × 703 = 21.48

For kg and meters/metres

  1. Divide your weight (kg) by your height (m).
    Example: 65kg ÷ 1.83m = 35.519
  2. Divide your answer from part 1 by your height again.
    Example: 35.519 ÷ 1.83 = 19.41

Note that you can convert between units of height with our height converter or our cm to feet converter.

BMI formula for men and women

The official formula for BMI was devised in the 1830s by Belgian mathematician Adolphe Quetelet.

Imperial BMI Formula

BMI = 703 × weight (lb) / [height (in)]2

Metric BMI Formula

BMI = weight (kg) / [height (m)]2

Learn more about how to use these formulae with our in-depth article on the BMI formula. An interactive BMI chart is also available to use.

What Is BMI?

The body mass index calculator measurement is the calculation of your body weight in relation to your height and is commonly used as an indicator of whether you might be in a risk category for health problems caused by your weight. Using a BMI calculator such as the one on this page, you enter your weight and height measurements.

Below are the BMI classifications for men and women established by the World Health Organization (WHO) and endorsed by leading organizations of health professionals. Reference: The practical guide: identification, evaluation, and treatment of overweight and obesity in adults - National Institutes of Health (NIH), National Heart, Lung, and Blood Institute (NHLBI).

Body Mass Index (kg/m2) Classification
less than 18.5: underweight
18.5 - 24.9: normal weight
25 - 29.9: overweight
30 - 34.9: class I obese
35 - 39.9: class II obese
40 upwards: class III obese

It is important to remember that BMI measurements do not make a distinction between whether you are male or female, whether you have a large or small body frame, whether you have high muscle mass and the areas in which fat is distributed around your body. So, someone who has a very muscular physique (a body builder, for example) may have a high BMI without having excess fat. For this reason, BMI is not an indicator of obesity on its own.

Some alternative methods to BMI, including the waist-hip ratio, are discussed in our article, 5 alternatives to BMI. There's also a good section about BMI on the CDC website.


As well as BMI, this website also features a BMR calculator that allows you to calculate your basal metabolic rate (the number of calories you might burn in a day if you are inactive).