Free BMI Calculator — Check Your Body Mass Index
Calculate your Body Mass Index instantly. Works with metric (cm/kg) and imperial (ft/in, lbs) units, shows your weight category on a color gauge, and tells you your healthy weight range. All calculations happen in your browser.
How to Use the BMI Calculator — Check Your Body Mass Index in 3 Steps
- Enter your height — in centimetres or feet and inches.
- Enter your weight — in kilograms or pounds.
- Click Calculate to see your BMI, WHO category (underweight, healthy, overweight, obese), and healthy weight range.
Frequently Asked Questions
What is a normal BMI?
According to the WHO, a normal (healthy) BMI for adults is 18.5 to 24.9. Below 18.5 is underweight, 25 to 29.9 is overweight, and 30 or above is classed as obese. For example, a BMI of 22.9 falls comfortably in the healthy range. These cut-offs apply to most adults aged 20 and over.
How is BMI calculated?
BMI is your weight in kilograms divided by the square of your height in metres. For example: 70 ÷ (1.75 × 1.75) = 70 ÷ 3.06 = 22.9. In imperial units, multiply weight in pounds by 703 and divide by height in inches squared. Our calculator accepts both metric and imperial units and does the maths for you.
Is BMI accurate for athletes and muscular people?
Not always. BMI cannot tell muscle from fat, so athletes with high muscle mass can score as 'overweight' while being very fit. The CDC notes BMI is a screening tool, not a diagnosis. If you lift weights regularly or are very muscular, consider body-fat percentage or waist measurement alongside BMI for a fuller picture.
What is the difference between BMI and BMI Prime?
BMI Prime is your BMI divided by 25, the upper limit of the healthy range. A BMI Prime of 1.0 means you are at the top of healthy; below 1.0 is underweight-to-healthy, above is overweight. For example, a BMI of 22.9 gives a BMI Prime of 0.92. It is simply a ratio that makes the healthy boundary easier to read.
How often should I check my BMI?
Checking once a month is plenty for most people — weight naturally fluctuates day to day with water and meals. Track the trend over months rather than reacting to a single reading. If your BMI moves into the overweight or obese range and stays there, consider speaking with a doctor or nutritionist.
What should I do if my BMI is above 25?
A BMI over 25 suggests reviewing diet and activity, but it is not a medical diagnosis on its own. Small sustainable changes — walking 30 minutes daily, cutting sugary drinks — move the number steadily. For example, losing 5 kg can drop BMI by nearly 2 points. Speak to a healthcare professional for personalised advice.
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