Free BMI Calculator
BMI Calculator works out body mass index from your height and weight in metric or US units and shows its WHO adult category, from underweight below 18.5 to obesity class III at 40 or more. It also gives the healthy weight range for your height. For ages 2 to 19 it gives the CDC BMI-for-age percentile and category instead.
- Formula:
- Weight (kg) ÷ height (m)²
- Normal range:
- 18.5–24.9 (WHO, adults)
- Ages 2–19:
- CDC BMI-for-age percentiles
- Price:
- Free
- Runs:
- Locally, in your browser
- Uploads:
- None: files never leave your device
- Account:
- Not needed
Quick answers
How is BMI calculated?
BMI is your weight in kilograms divided by the square of your height in meters. With US units, pounds and inches are converted first.
What is a healthy BMI?
For adults, the World Health Organization classes 18.5 to 24.9 as normal weight. Below is underweight, 25 to 29.9 overweight and 30 or more obesity.
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How to use the BMI Calculator
- Choose metric (cm, kg) or US units (feet, inches, pounds).
- Enter your height and weight; add your age if you want the right guidance for children and teens.
- Read your BMI, its WHO category on the colored scale and the healthy weight range for your height.
Credits & open source
Built from scratch on web standards. Thank you to the people who make these projects.
Web platform APIs used: Intl.
- CDC BMI-for-age growth chart data (extended BMI-for-age charts, 2022) by Centers for Disease Control and Prevention, National Center for Health Statistics (Public domain (US government work)) — L, M, S parameters for BMI-for-age percentiles of ages 2 to 19 (bmi-age-2022.csv)
Full license texts: third-party notices · all credits
Frequently asked questions
Can I use it for children?
Yes, from 2 to 19 years: enter the age (years and months) and the sex, and it shows the BMI-for-age percentile, the z-score and the category from the CDC growth charts (underweight below the 5th percentile, overweight from the 85th, obesity from the 95th). It is a screening measure, so ask a pediatrician to interpret it. BMI is not used under age 2.
Is BMI accurate for everyone?
No. It does not distinguish muscle from fat, so it can mislead for athletes, older adults and pregnant people. It is a screening number, not a diagnosis.