BMI Calculator
Formula
Metric: BMI = weight (kg) / height (m)²
Imperial: BMI = (weight (lbs) / height (in)²) × 703
How to Use This Calculator
Measure with consistent tools
Use a calibrated scale for weight and a stadiometer or wall ruler for height. Enter the values using the same unit system.
Toggle between metric and imperial units
Switch the calculator to kilograms/centimeters or pounds/inches as needed—your entries will be recalculated instantly.
Interpret the BMI category
Compare the BMI result with standard categories to screen for underweight, healthy weight, overweight, or obesity.
BMI Formula
BMI = Weight ÷ Height²
- Metric: BMI = weight (kg) ÷ [height (m)]²
- Imperial: BMI = weight (lb) ÷ [height (in)]² × 703
- Interpret results alongside other assessments such as waist measurements and body fat tests.
Understanding BMI
Body Mass Index (BMI) screens for weight categories that may lead to health problems. It does not directly measure body fat, but it correlates with more sophisticated assessments and is widely used in clinical practice.
Underweight
BMI < 18.5
Normal weight
18.5 ≤ BMI < 25
Overweight
25 ≤ BMI < 30
Obesity
BMI ≥ 30
Reminder: BMI is a screening tool. Muscular individuals or older adults may require additional measurements for an accurate picture of health.
Frequently Asked Questions
Is BMI accurate for athletes?
BMI may overestimate body fat in people with high muscle mass. Combine BMI with body fat tests or waist measurements for better insight.
What BMI range is considered healthy?
For most adults, 18.5–24.9 indicates a healthy BMI. However, individual factors like age, muscle mass, and ethnicity matter.
How often should I check my BMI?
Quarterly checks are sufficient for most people. Monitor more frequently if you are actively changing your weight or under medical supervision.
Does BMI work for children?
Children and teens require BMI-for-age percentiles. Use a pediatric-specific calculator for accurate interpretation.