BMI Calculator

Calculate your Body Mass Index (BMI) to check if you're at a healthy weight.

Please Note: The BMI Calculator provides general information only and is not a substitute for professional medical advice. Please consult your GP or healthcare provider for personalised guidance about your health.

Body Mass Index (BMI) is a measure of body fat based on your weight and height. It's a useful indicator to assess whether you are at a healthy weight for your height.

This calculator is designed for adults 18 years and older. For children and teens, please consult a healthcare professional.

ft
in
BMI calculator is for adults 18+
Optional - for statistical purposes only

How to Use the BMI Calculator

  1. Select your preferred unit system (Metric or Imperial)
  2. Enter your weight (in kilograms or pounds)
  3. Enter your height (in centimeters or feet/inches)
  4. Enter your age (must be 18 or older)
  5. Optionally select your gender (for statistical purposes)
  6. Click the "Calculate BMI" button

About BMI (Body Mass Index)

BMI is a simple calculation using a person's height and weight. The formula is BMI = kg/m² where kg is a person's weight in kilograms and m² is their height in meters squared.

BMI Categories:

  • Underweight: BMI less than 18.5
  • Normal weight: BMI 18.5 to 24.9
  • Overweight: BMI 25 to 29.9
  • Obesity: BMI 30 or greater

Limitations of BMI

While BMI can be a useful tool for identifying potential weight issues, it does have limitations:

  • It doesn't account for differences in body composition (muscle vs. fat)
  • It doesn't consider the location of body fat
  • It may not be accurate for athletes, elderly individuals, or pregnant women
  • It doesn't account for ethnic and racial differences in body composition

Frequently Asked Questions

BMI (Body Mass Index) is a simple calculation using your height and weight to estimate body fat. The formula is weight (kg) divided by height (m) squared. It's a screening tool used to identify potential weight problems in adults.

A healthy BMI is generally between 18.5 and 24.9. Below 18.5 is considered underweight, 25-29.9 is overweight, and 30 or above is classified as obese. However, BMI doesn't account for muscle mass, age, or body composition.

BMI has limitations. It may overestimate body fat in athletes and muscular individuals, and underestimate it in older people who have lost muscle mass. It also doesn't account for ethnic differences in body composition or where fat is stored on the body.

Either works equally well. In the UK, people commonly know their weight in stones and pounds and height in feet and inches. Our calculator supports both metric (kg/cm) and imperial (lb/ft/in) units with the same accuracy.

If your BMI indicates you're underweight, overweight, or obese, consider consulting a healthcare professional. They can assess your overall health, consider factors BMI doesn't measure, and recommend appropriate lifestyle changes or treatments if needed.

Related Tools

Disclaimer

This calculator is provided for educational and informational purposes only. It is not intended to be a substitute for professional medical advice, diagnosis, or treatment.

  • Always seek the advice of a qualified healthcare provider with any questions regarding a medical condition.
  • Never disregard professional medical advice or delay seeking it because of information from this tool.
  • Clinical decision-making should always incorporate the full clinical context, patient preferences, and local protocols.
  • The creators of this tool accept no liability for decisions made based on its output.

If you are a patient: please discuss any results with your healthcare provider. This tool is designed for use by medical professionals and may not be appropriate for self-assessment.