How to Calculate BMI in the UK: Step-by-Step Guide

Introduction

Health calculators turn guidelines into numbers that fit your body. They're a starting point for a conversation with your GP, not a diagnosis.

This guide explains how to calculate bMI in the UK, step by step. Calculate your Body Mass Index using feet, inches, stone and pounds. You'll see the formula, a fully worked example and practical tips for UK readers.

What this calculation covers

Calculate your Body Mass Index using feet, inches, stone and pounds.

Understanding your figures can help you set sensible fitness goals, track change over time and know when to ask a health professional for advice.

The method and formula

BMI is weight in kg divided by height in metres squared. The NHS adult ranges are: under 18.5 underweight, 18.5–24.9 healthy, 25–29.9 overweight and 30 or more obese. BMI doesn't account for muscle, age or ethnicity.

Every figure on our bMI Calculator (Stone and Pounds) follows this method, so you can check the working yourself.

Worked example

Here's a typical example using these figures:

Running them through the method gives:

The headline figure is your bmi: 24.1. Change any input and the result will move with it.

How to use the calculator

1. Enter or choose height (feet).
2. Enter or choose height (inches).
3. Enter or choose weight (stone).
4. Enter or choose weight (pounds).
5. Read your results. The main figure is shown at the top, with a breakdown underneath.
6. Try different values to compare scenarios side by side.

Tips for UK readers

• The NHS uses BMI as a screening tool, but waist measurement also matters.
• Estimates like BMR and body fat can vary by 5–10% from lab measurements.
• Track trends over weeks rather than day-to-day changes.
• Speak to your GP or midwife about any results that worry you.

Frequently asked questions

What's the quickest way to work out bMI?

Use our free bMI Calculator (Stone and Pounds). It applies this method automatically: BMI is weight in kg divided by height in metres squared. The NHS adult ranges are: under 18.5 underweight, 18.5–24.9 healthy, 25–29.9 overweight and 30 or more obese. BMI doesn't account for muscle, age or ethnicity.

Is this medical advice?

No. These tools give general estimates. For medical advice, speak to your GP, pharmacist or NHS 111.

Can I use these for children?

No. Children's BMI and health measures use age- and sex-specific charts. Use the NHS healthy weight calculator for children.

Why use stone and pounds?

Many people in the UK still think in stone and pounds, so we accept those units and show metric too.

Summary

To work out bMI, follow the method above: BMI is weight in kg divided by height in metres squared. For a quick, accurate answer with your own figures, use the calculator.

Next, read BMI: Common Mistakes, Tips and FAQs.