Skip to main content
LibraTool logoLibraTool

Free BMI Calculator

Calculate your Body Mass Index in metric or imperial units. See your BMI category, healthy weight range, and where you fall on the scale.

Works offline once loaded
Cut-offs

Enter your weight and height to see your BMI.

Note: BMI is a population-level screening tool, not a medical diagnosis. It does not account for muscle mass, bone density, age, sex, or fat distribution. Results may be misleading for athletes, older adults, and some ethnic groups. Consult a healthcare professional for personalised advice.

Common uses

  • Track BMI During Weight LossMonitor your BMI progress as you work toward a healthy weight range.
  • Calculate BMI for Fitness GoalsUse BMI as one data point for setting realistic fitness and body composition goals.
  • BMI for Annual Health ChecksCalculate your BMI for doctor appointments, insurance forms, and annual wellness screenings.
  • Understanding BMI for AdultsLearn what your BMI number means, what category you fall into, and what the WHO guidelines say.
  • BMI for Travel and Life InsuranceCalculate your BMI for travel insurance, life insurance, and medical forms that require this measurement.

How It Works

This BMI calculator runs entirely in your browser using a hand-written formula β€” no library, no server call. Every number updates the instant you type, computed live in a React useMemo hook using the standard WHO formula (weight in kg divided by height in metres squared).

  1. 1
    Unit conversion
    If you enter imperial measurements, the tool converts pounds to kilograms (Γ— 0.453592) and feet/inches to metres (total inches Γ— 0.0254) before any calculation runs. Metric values pass through unchanged.
  2. 2
    BMI and companion indices
    The core formula divides your weight in kg by the square of your height in metres. The same height and weight values feed two companion metrics: BMI Prime (your BMI divided by 25, where 1.0 means exactly at the upper boundary of normal) and the Ponderal Index (weight divided by height cubed, in kg/mΒ³), which scales better for very tall or very short individuals.
  3. 3
    Category and healthy weight range
    Your BMI is matched against the six WHO categories (Underweight through Obese Class III) using a simple threshold lookup. The tool then works the formula backwards from the 18.5 and 24.9 boundaries to show the healthy weight range in kg or lbs for your exact height.
  4. 4
    Visual scale and delta feedback
    Your BMI is mapped onto a 10–40 colour gradient and a marker is positioned at ((bmi βˆ’ 10) / 30) Γ— 100 percent along the bar. A plain-language line tells you how many kg or lbs you are above or below the healthy range, or confirms you are within it.

BMI is a personal health metric, but nothing you enter here leaves your device β€” all arithmetic runs in your browser with no network requests.

Related Tools

πŸ“‰

Body Fat Calculator

Estimate your body-fat percentage with the U.S. Navy tape-measure method or a BMI-and-age estimate β€” with your fitness category, fat mass, and lean body mass. Metric or imperial, private and free.

Try it
βš–οΈ

Ideal Weight Calculator

Find your healthy weight range for your height plus the classic ideal-body-weight formulas (Devine, Robinson, Miller, Hamwi). Add your weight for your BMI and the gap to a healthy weight. Metric or imperial, private and free.

Try it
πŸ“

Unit Converter

Convert between units of length, weight, temperature, area, volume, and more.

Try it

Frequently Asked Questions