Use our free health calculators to estimate adult BMI, interpret BMI-for-age for children and teenagers, or look up BMI using metric and imperial charts. Each tool explains its formula, supported age range and important limitations.
Start with the calculator that matches the person’s age. Adult BMI categories apply to people aged 20 and older. For ages 5–19, use the separate girls or boys BMI-for-age calculator.
BMI calculators
Adult BMI Calculator
Calculate adult BMI using metric or imperial measurements and review the corresponding adult category.
Girls BMI Calculator
Estimate BMI-for-age percentile ranges for girls aged 5–19 using WHO 2007 reference data.
Boys BMI Calculator
Estimate BMI-for-age percentile ranges for boys aged 5–19 using WHO 2007 reference data.
BMI formulas and charts
BMI Formula
Learn the metric and imperial formulas with unit conversions and worked examples.
Add the calculator to WordPress
The BMI Calculator WordPress plugin and shortcode guide explains installation, display settings and shortcode parameters for adding the adult calculator to another WordPress site.
How to use these health calculators
- Use current, accurately measured height and weight.
- Choose the calculator for the correct age and sex-specific reference where applicable.
- Read the formula, reference source and limitations provided with the result.
- Discuss concerning or unexpected results with a qualified healthcare professional.
Important: These tools provide screening estimates and general information, not diagnoses. BMI does not directly measure body fat or distinguish fat from muscle and bone. Adult information follows CDC BMI guidance; child and teen calculators use the WHO 2007 growth reference for ages 5–19.
Directory and reference information reviewed 29 August 2026.