Free BMI Calculator — Free Health Calculator
Calculate your Body Mass Index instantly.
How to Use BMI Calculator — 3 Simple Steps
Enter your details
Type your height and weight. Use the toggle to switch between metric (kg/cm) and imperial (lbs/ft/in) units.
Calculate your BMI
Click Calculate BMI. Your BMI score appears instantly along with your category: Underweight, Normal, Overweight, or Obese.
Understand your result
Read the colour-coded scale showing where your BMI falls and the healthy range for your height. Results update when you adjust inputs.
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Frequently Asked Questions About BMI Calculator
For most adults, a BMI of 18.5 to 24.9 is considered healthy. Below 18.5 is underweight, 25 to 29.9 is overweight, and 30 or above is classified as obese. These thresholds apply to most adults, though athletes may differ.
Divide your weight in kilograms by your height in metres squared. For example: 70 kg ÷ (1.75 × 1.75) = 22.9 BMI. In imperial: multiply weight in pounds by 703, then divide by height in inches squared.
Not always. BMI measures weight relative to height but cannot distinguish muscle from fat. Athletes with high muscle mass often show an "overweight" BMI despite having low body fat. Use BMI as a general screening tool, not a definitive health measure.
A BMI below 17.5 is considered severely underweight and is associated with serious health risks including bone loss, immune system weakness, and heart problems. If your BMI is below 18.5, consider speaking with a healthcare professional.
Children use age- and sex-specific BMI percentile charts, not standard adult thresholds. A child's BMI is healthy if it falls between the 5th and 85th percentile for their age. Always use a paediatric BMI calculator for anyone under 18.
For general health tracking, checking BMI every 3 to 6 months is sufficient. BMI changes slowly with lifestyle — it is not a day-to-day measure. Focus on long-term trends rather than individual readings.