We use cookies to allow us and selected partners to improve your experience and our advertising. By continuing to browse you consent to our use of cookies. You can understand more and change your cookies preferences here.

Calculating your BMI

By Haddi Browne

BMI is considered the best assessment of an adult’s weight - read on to find out how to calculate yours, and what it means.

Put us to the test

Our Test Labs compare features and prices on a range of products. Try Which? to unlock our reviews. You'll instantly be able to compare our test scores, so you can make sure you don't get stuck with a Don't Buy.

BMI stands for Body Mass Index, which takes into account your height and weight to give you an indication of if you're overweight, underweight or within a healthy range.

How to work out your BMI

Divide your weight (in kilograms) by your height (in metres), and then divide this answer by your height again. This number lets you see which of the following weight ranges you fit in, in relation to your height:

  • Below 18.5 - if your BMI is under 18.5, you're considered underweight.
  • 18.5-24.9 - this is the healthy BMI range for your height.
  • 25-29.9 - if your BMI is in this range, it means you might be heavier than healthy for someone of your height. With excess weight comes an increased risk of heart disease, stroke and Type 2 diabetes.
  • 30 or more - those with a BMI of more than 30 are classified as obese, and therefore could be at greater risk of developing weight-related health problems.

Body fat analyser scales that calculate BMI

We've tested and reviewed a range of body fat analyser scales, many of which can automatically calculate your BMI on top of other useful information such as your body fat and body water percentages.

This type of bathroom scale enables you to input your height, which it then combines with your weight (in either imperial or metric units) when you step on the scales to calculate your BMI. Most also recognise and remember different users, so you should only have to put this information in once.

However, our lab tests tests have found that some body fat analysers give less accurate weight readings than others, meaning that they’ll give you a less accurate BMI measurement.

Find a body fat analyser that gives accurate weight measurements and body fat percentages by heading to our best bathroom scale recommendations.

Limitations of BMI

The NHS considers BMI the best way to quickly assess an adult’s weight, although it’s not without its flaws.

The following factors show why BMI isn’t always the perfect universal assessment of weight:

  • Pregnancy - pregnant women naturally gain weight due to their growing baby, so BMI readings won't be accurate.
  • Children - with children, age and sex need to be taken into account as well as height and weight.
  • Muscle - your level of muscle mass isn't taken into consideration with BMI measurements. This means that people who are particularly active may be given an inaccurate reading.
  • Ethnicity - research has shown that those of south Asian or Chinese descent have an increased risk of developing Type 2 diabetes. It's therefore recommended that those of south Asian or Chinese descent keep their BMI reading below 23 to reduce this risk. Although the evidence is less definite, black people are also advised to maintain a BMI below 25 to reduce the risk of developing Type 2 diabetes.

Your chance of developing heart disease, stroke and Type 2 diabetes increases if your BMI is more than 25, though there are plenty of other health factors that can play a part in this as well. It's advisable to maintain a healthy weight, follow a balanced diet and exercise regularly to help reduce this risk.


Related products

See all bathroom scales