BMI Calculator — Free Online Tool
Find your Body Mass Index and weight category using metric or imperial units.
About BMI Calculator
The BMI Calculator estimates your Body Mass Index from your height and weight and tells you which standard weight category you fall into. You can switch between metric (cm, kg) and imperial (ft/in, lb) units, so it works wherever you are in the world.
BMI is a quick screening number used by health organisations to flag whether your weight may be in a healthy range for your height. This tool gives you that number instantly and privately, with all calculations done in your browser.
How to Use BMI Calculator
- Choose metric or imperial units from the dropdown.
- Enter your height and weight in the matching fields.
- Click "Calculate BMI" to see your index.
- Read your BMI value and the colour-coded weight category below it.
Key Features
Supports both metric and imperial units
Instant weight category with colour coding
Accurate BMI formula used by health bodies
Clean, mobile-friendly input fields
Private: nothing is sent to a server
Frequently Asked Questions
What do the BMI ranges mean?
A BMI below 18.5 is classed as underweight, 18.5 to 24.9 as normal weight, 25 to 29.9 as overweight, and 30 or above as obese.
How is BMI calculated?
BMI equals your weight in kilograms divided by the square of your height in metres. The imperial mode converts feet, inches and pounds before applying the same formula.
Is BMI accurate for everyone?
BMI is a general screening tool and does not account for muscle mass, age or body composition, so very muscular people may read as overweight. Treat it as a guide, not a diagnosis.
Should I rely on BMI alone for health decisions?
No. BMI is a starting point. For health decisions, combine it with other measures and advice from a qualified healthcare professional.