BMI Calculator
Calculate your Body Mass Index in metric or imperial units, with category.
Result
What is BMI Calculator?
BMI, or Body Mass Index, is a screening number that expresses the relationship between a person's weight and height as a single value. It is calculated as weight in kilograms divided by height in meters squared (kg/m²), or equivalently as 703 times weight in pounds divided by height in inches squared. The result is mapped onto the World Health Organization's standard adult categories: Underweight below 18.5, Normal weight from 18.5 to 24.9, Overweight from 25 to 29.9, and Obese at 30 or above. BMI is used widely in clinical, fitness, and research settings as a quick way to flag potential weight-related health risk at a population level. It is a screening indicator rather than a diagnosis, since it cannot distinguish muscle from fat and does not account for age, sex, or body composition.
How to Use BMI Calculator
- Choose Metric (kg/cm) or Imperial (lb/in) units.
- Enter your weight and height — the BMI updates instantly.
- Check the category label (Underweight, Normal weight, Overweight, Obese) below the number.
- Switching units keeps your inputs in sync, so you don't have to re-enter anything.
Examples
Metric
Input: 70 kg, 175 cm
Output: 22.9 — Normal weight
Imperial
Input: 154 lb, 69 in (5'9")
Output: 22.7 — Normal weight
Common Mistakes
- Entering height in the wrong unit for the selected system (e.g. typing feet instead of inches under Imperial) — the result will be wildly off since height is squared in the formula.
- Treating BMI as a precise medical diagnosis rather than a general screening indicator — it doesn't account for muscle mass, bone density, or fat distribution.
- Comparing BMI directly across very different body types (e.g. a bodybuilder vs. a sedentary adult) and drawing the same health conclusion from the same number.
Why Use This Tool
- Supports both Metric and Imperial units with a one-click toggle.
- Instant result with the standard WHO category shown alongside the number.
- Runs entirely client-side — no data ever leaves your browser.
- No sign-up, no ads blocking the result, no daily limit.