About BMI and how to use this tool

What is BMI?

Body Mass Index (BMI) is a measure that uses your height and weight to give a number. It is used as a screening tool to indicate whether an adult’s weight might put them at higher risk of some health conditions. BMI does not diagnose illness and does not measure body fat directly.

How to use this calculator

Choose how you want to enter your height (feet and inches, cm, or metres).
Choose how you want to enter your weight (stones and pounds, kg, or lb).
Enter your height and weight. Optionally add age, sex, and ethnicity for more tailored guidance.
Select Show my results to see your BMI, category, and next steps.

What you get

Your BMI number and category (e.g. healthy weight, overweight).
A colour-coded gauge and a BMI table by height and weight.
Plain-language guidance and practical next steps.
Links to NHS and NICE resources. This tool is independent and not part of the NHS.

Before you start

BMI is a screening tool. It does not diagnose symptoms. If you are worried about your weight or health, speak to a pharmacist or GP.

This calculator is for adults aged 18 and over.

Do not use this tool if any of the following apply:

You are under 18.
You are pregnant.
You have been diagnosed with an eating disorder, or think you may have one.
You have a condition that affects your height.

I confirm none of the above apply, and I am 18 or over.

How do you want to enter your height?

Feet Inches e.g. 5 ft 9 in

How do you want to enter your weight?

Stones Pounds e.g. 11 st 0 lb

Target weight (optional)

If you have a target in mind, add it now and we will show how your BMI could change. You can skip this.

Add a target weight

Optional details

Age (optional)

Sex (optional)

Used for context in the explanation only. It does not change your BMI score.

Ethnicity setting How ethnicity can affect BMI interpretation

Your BMI is —, which sits in the — category.

Your result

—

Details

Healthy BMI range: –

Healthy weight range for your height: –

Target weight

Optional. Shows how your BMI could change.

Calculated locally. BodyMI does not store your target weight.

BMI table

Use this table to see how BMI changes by height and weight. It is a guide, not a diagnosis.

What does this mean

What can you do now

Waist to height ratio (optional)

Measuring your waist can help you understand whether you are carrying too much weight around your tummy. NHS guidance suggests aiming to keep your waist size to less than half your height.

Waist measurement

How to measure your waist

Measure around your waist, midway between the bottom of your ribs and the top of your hips.
Keep the tape snug but not tight, and breathe out naturally.
Take the measurement against bare skin where possible.

Calculated locally in your browser. We do not store your measurements.

NHS waist to height ratio tool

Next steps

A few practical options based on your result. Choose what feels realistic for you.

Useful links

NHS guidance

References (APA)

This tool provides general information for adults aged 18 and over. It does not replace clinical advice. If you are under 18, pregnant, managing a long-term condition, or concerned about your weight or health, speak to your GP or local healthcare service.

Other UK tools you may find helpful

These links open trusted UK sources. BodyMI is independent and not part of the NHS.

When to seek help

If you are worried about your weight or general health, speak to your GP or pharmacist. For urgent (non-emergency) advice, call NHS 111. If you think it is an emergency (for example chest pain, severe breathing difficulty, or signs of stroke), call 999 or go to A&E.

Save or share

Download a one-page PDF, email your summary to a clinician, or print directly.

Everything runs locally. BodyMI does not send emails and does not receive your data.

Advanced UK BMI Calculator