Overview
Body mass index (BMI) uses weight and height to estimate whether weight is in a healthy range. It is a quick screening tool, but it does not measure body fat or muscle, so it should be read alongside other factors.
Formula
BMI = weight (kg) ÷ height (m)². In imperial units: BMI = 703 × weight (lb) ÷ height (in)².
How it works
Choose your unit system
Metric with kilograms and centimeters, or imperial with pounds and inches.
Enter weight and height
Use current measurements without shoes.
Read the index and category
The calculator also shows the healthy weight range for your height.
Worked examples
Example 1: 70 kg and 170 cm
BMI = 70 ÷ 1.7² = 24.2, a healthy weight.
Example 2: 90 kg and 170 cm
BMI = 90 ÷ 1.7² = 31.1, within the obesity range.
Frequently asked questions
Is BMI accurate for everyone?
No. It can overestimate body fat in muscular athletes and underestimate it in older adults. Use it as a screening tool only.
What is a healthy BMI range?
Adults are usually classified as under 18.5 underweight, 18.5–24.9 healthy, 25–29.9 overweight, and 30 or above obese.
Can it be used for children?
Children use age- and sex-specific growth charts, not the adult BMI categories.
Is it suitable during pregnancy?
BMI is not appropriate for weight assessment during pregnancy. Follow your doctor's guidance.
This calculator is for educational and informational purposes only and is not a substitute for professional advice.