Paper with My BMI = Weight over Height squared written on it, with a tape measure

How to calculate your BMI

Body Mass Index (BM) is a useful benchmark for bodyweight and health. You might even have had yours measured by your GP. But how can you calculate your BMI at home? And what does the number really mean?

What is BMI?

BMI is just one way of calculating whether your body mass is healthy for your height. BMI is more meaningful than just tracking your bodyweight, but it's less accurate than calculating what your mass it made up of.  Your muscle mass, bone density, body fat and water weight are all important markers of health. However, it’s not easy to find all of that out so BMI is an easy calculation which gives a useful benchmark for health.

Here's how to work out your BMI, and what the numbers mean.

How to calculate BMI

Calculating your BMI is a simple question of measuring your height, weighing yourself, and then doing a quick equation:

Divide your weight in kilograms by your height in metres.

Divide that answer by your height.

That’s your BMI!

Is your BMI healthy?

< 18.5 BMI is considered underweight.

18.5-24.9 is considered normal.

25-29.9 is labelled as overweight.

And a BMI of 30 or more is considered obese.

But remember that BMI can only measure your mass, and doesn’t take into account muscle mass. If you are very slight with a small build, and thin wrist and ankles, you may have a low BMI yet be healthy. And if you carry a lot of muscle mass and have an athletic build, you could have an overweight BMI but actually be in good health. BMI is just one indication of health and should be considered alongside lots of other factors.

If you are worried about your BMI and want to know if you should lose or put on weight to improve your health, talk to your Doctor.

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