BMI Calculator — Free Body Mass Index Calculator

This free BMI calculator instantly computes your Body Mass Index from your height and weight, in either metric or imperial units. You'll see your numeric BMI value, the standard WHO weight category, and a quick explanation of what that range means.

Why use this BMI Calculator?

  • Supports both metric (kg/cm) and imperial (lbs/ft/in) inputs
  • Instant BMI result with color-coded weight category
  • Shows the healthy BMI range for your height
  • No data sent anywhere — all math runs in your browser

How to use the BMI Calculator

  1. Choose your unit system: Select metric (kilograms and centimeters) or imperial (pounds, feet, and inches) using the toggle at the top.
  2. Enter your height: Type your height — for imperial, enter feet and inches separately, for example 5 ft 9 in.
  3. Enter your weight: Type your current weight in kilograms or pounds.
  4. View your BMI and category: Your BMI number and category (Underweight, Normal, Overweight, or Obese) appear immediately with a brief explanation.

Frequently Asked Questions

How is BMI calculated?

BMI is weight in kilograms divided by height in meters squared (kg/m²). In imperial units the formula is (weight in lbs × 703) ÷ (height in inches)². For example, someone who is 5'9" (175 cm) and 160 lbs (72.6 kg) has a BMI of roughly 23.6.

What are the standard BMI categories?

The World Health Organization defines: Under 18.5 as Underweight, 18.5–24.9 as Normal weight, 25.0–29.9 as Overweight, and 30.0 and above as Obese. These thresholds apply to most adults but differ slightly for children and certain ethnic groups.

Is BMI accurate for athletes or muscular people?

BMI has a well-known limitation: it doesn't distinguish between fat mass and muscle mass. A very muscular athlete may have a BMI in the 'Overweight' range despite having very low body fat. Clinicians often pair BMI with waist circumference or body fat percentage for a fuller picture.

Does BMI apply to children?

Children use age- and sex-specific BMI percentiles rather than the fixed adult thresholds. The CDC and WHO publish separate charts for children aged 2–19. This calculator uses the standard adult formula and is not intended for pediatric use.

What BMI is considered healthy?

A BMI between 18.5 and 24.9 is considered normal or healthy weight for most adults. However, your ideal healthy weight depends on factors like age, muscle mass, and bone density, so always discuss your specific situation with a healthcare provider.

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