Health & Fitness
BMI Calculator
Rates & guidance reviewed
Body Mass Index (BMI) is a simple screening measure that relates weight to height. It is widely used in the UK as a starting point for discussing healthy weight ranges with a GP or clinician.
This free BMI calculator supports metric (kg, cm) and imperial (st/lb, ft/in) inputs and classifies the result using standard WHO adult categories. It runs entirely in your browser.
BMI does not account for muscle mass, bone density, age or ethnicity-specific guidance. It is not a diagnosis — speak to a healthcare professional for personalised advice.
Interactive tool
Results
Adult BMI categories only. Not a diagnosis — speak to a GP for personal advice. Not suitable for children without clinical charts.
How to use this tool
- Choose metric or imperial units.
- Enter your height and weight.
- View your BMI value and category.
- Read the notes on limitations and when to seek advice.
Understanding adult BMI categories
For most adults, BMI under 18.5 is classed as underweight; 18.5–24.9 as a healthy weight range; 25–29.9 as overweight; and 30 or above as obesity (with further clinical subclasses sometimes used). These cut-offs are population screening tools, not personal diagnoses.
NICE and NHS guidance note that BMI may need careful interpretation for athletes, older people, and some ethnic groups where health risk can differ at the same BMI. Waist circumference and clinical assessment often add useful context.
Official sources & further reading
Always confirm rates, bands and eligibility on official pages. Our tools are simplified estimators for guidance only.