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BMI Calculator

Quickly find out your BMI and see if you're eligible for BeeZee Bodies programmes

What is BMI?

You can use this calculator to work out your BMI, or ‘body mass index’.

This is a widely used measurement to determine whether or not you’re a healthy weight, and it should only take a few seconds.

BMI measurements do have some limitations (more on this below), but they’re a good basic indicator of health for most people.

What your BMI means

Whether you’re a healthy weight or not is calculated differently for adults and children.

For adults

  • A BMI of less than 18.5 falls into the underweight range
  • A BMI of between 18.5 – 25 falls into the healthy weight range
  • A BMI of between 25 – 30 falls into the overweight range
  • A BMI of more than 30 falls into the obese range


For children

Unlike for adults, BMI for children depends on age and sex as well as height and weight. Children’s healthy weight ranges are also calculated differently, using ‘centiles’.

For example, if 99% of people of your age, sex and height weigh less than you, then you’re in the 99th centile. If 80% of them weigh less than you, you’re in the 80th centile. And so on.

  • If a child is on the 2nd centile or below, they’re considered to be underweight
  • Being between the 2nd and 90th centiles would put them in the healthy weight range
  • A child at the 91st centile or above would fall into the overweight range
  • While being in the 98th centile or above would place them in the very overweight range

What are the limitations of BMI?

While BMI can give a rough idea of body size, it isn’t a perfect representation of an individual’s health and has some limitations:

  • Some particularly muscular adults will have a BMI that puts them in the overweight range, even if they have very little fat
  • Older adults and women can sometimes have too much fat even if they’re in the healthy weight range
  • The results are not valid for pregnant women (who should use their pre-pregnancy weight to calculate their BMI)
  • BMI results also do not apply to people with eating disorders, who should talk to their GP instead


If you’re unsure or don’t think your BMI results are accurate, you could also measure your body fat to get a better overall picture of your health. But that’s not something you can do in 30 seconds with an online calculator!

Eligibility for BeeZee Bodies programmes

Because we’re funded by local councils and the Office for Health Improvement and Disparities, most of our programmes have eligibility criteria.

For simplicity, these eligibility criteria are usually based on your BMI, and the exact requirements will be listed on the webpage for each programme.

Check out our programmes