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Health & Fitness
BMI Calculator
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
Your BMI24.2
CategoryHealthy weight
Adult BMI categories only. Not a diagnosis — speak to a GP for personal advice. Not suitable for children without clinical charts.
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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.
Frequently asked questions
How is BMI calculated?
BMI = weight (kg) ÷ height (m)². Imperial inputs are converted to metric before calculation.
What are the standard adult BMI categories?
Underweight: under 18.5; Healthy weight: 18.5–24.9; Overweight: 25–29.9; Obesity: 30 and above (with further subclasses sometimes used clinically).
Is BMI accurate for athletes?
Athletes and people with high muscle mass may have a high BMI without excess body fat. Other measures (waist circumference, body composition) may be more informative.
Does this work for children?
This tool uses adult categories. Children’s BMI is interpreted with age- and sex-specific centile charts — use NHS resources for under-18s.
Is my health data stored?
No. Height and weight never leave your device.