BMI Calculator
Calculate your Body Mass Index using metric or imperial units. See your BMI category, healthy weight range, target weight difference, body-shape context and waist-to-height ratio guidance.
Health disclaimer
This calculator is for general information only and is not medical advice. Speak to a qualified health professional before making major diet, exercise or health decisions.
Calculator
Enter your height in centimetres.
Enter your weight in kilograms.
Enter your height in feet and inches.
Enter your weight in stones and pounds.
BMI categories here are intended for adults.
BMI formula is the same, but context can differ.
Used for waist-to-height ratio context.
Used to estimate a target weight.
Adjustment context
BMI is a screening tool, not a diagnosis. Use these options to add context to the interpretation.
Result breakdown
Personalised interpretation
How BMI is calculated
BMI stands for Body Mass Index. It compares weight against height and gives a simple screening number for adults.
For adults, the common BMI categories are: below 18.5 underweight, 18.5 to 24.9 healthy weight, 25.0 to 29.9 overweight, and 30.0 or above obese.
The healthy weight range is calculated by rearranging the same formula using BMI 18.5 and 24.9 for your height.
Note: BMI does not directly measure body fat. It can be less accurate for children, pregnant people, older adults, very muscular people, some disabled people and people from backgrounds where health-risk thresholds may differ.
When BMI can be misleading
High muscle mass
Athletes or strength-trained people can have a high BMI because muscle is dense, even when body fat is not high.
Low muscle mass
A person may have a “healthy” BMI but still have low muscle mass or higher body fat, especially with low activity levels.
Children and teenagers
Children need age- and sex-specific centile charts rather than adult BMI categories.
Pregnancy
BMI is not suitable for judging weight status during pregnancy because healthy weight gain is expected.
Practical ways to use your BMI result
- •Use it as a starting point. BMI is useful for a quick screening result, not a complete health assessment.
- •Compare it with waist-to-height ratio. Waist size can add useful context around central body fat.
- •Look at trends over time. A gradual change in BMI can be more useful than a single reading.
- •Consider strength and fitness. Weight alone does not show muscle, cardiovascular fitness, blood pressure or blood markers.
Common questions
Is BMI accurate?⌄
What is a healthy BMI?⌄
Why include waist-to-height ratio?⌄
Can BMI be high if I am muscular?⌄
Sources and assumptions
This calculator is designed as a general adult screening tool. It uses the standard BMI formula and common adult BMI category thresholds. It is for general information only, is not medical advice, and should not replace advice from a GP, dietitian, nurse, pharmacist or other qualified healthcare professional.
- BMI formula: BMI is calculated as weight in kilograms divided by height in metres squared: BMI = kg ÷ m². Imperial entries are converted into metric units before the calculation.
- Adult BMI categories: the category thresholds used are based on common NHS and CDC adult guidance: underweight below 18.5, healthy weight 18.5 to 24.9, overweight 25.0 to 29.9, and obesity 30.0 or above. Obesity class ranges are also shown for additional context.
- Healthy weight range: the healthy range is estimated by rearranging the BMI formula using BMI 18.5 and 24.9 for the user’s height. This gives an approximate weight range rather than a personalised clinical target.
- Waist-to-height ratio: the waist-to-height ratio guidance is based on the principle that waist size should generally be less than half of height. NICE guidance also uses waist-to-height ratio categories to help assess central adiposity in adults, particularly when BMI is below 35 kg/m².
- Children and teenagers: adult BMI categories are not suitable for children and teenagers. Children need age- and sex-specific BMI centiles. This page is primarily intended for adult use.
- Limitations: BMI does not directly measure body fat, muscle mass, bone density, ethnicity-related risk differences, pregnancy, fluid retention, disability-related body composition differences, or overall fitness. It can be misleading for very muscular people, older adults, pregnant people and some medical situations.
- Result interpretation: the result should be treated as a quick screening estimate. If your result concerns you, or if you have symptoms, a medical condition, an eating disorder history, are pregnant, or are under 18, use official health guidance and speak to a healthcare professional.