BMI Calculator
Calculate adult BMI from metric or US measurements, show the standard BMI category and explain the limits of BMI as a screening measure.
Calculate adult BMI
Enter height and weight to calculate body mass index (BMI). This tool is intended for adults age 20+ and is a screening calculation, not a diagnosis.
BMI formula for adults
BMI = weight in kilograms ÷ height in metres squared. For US measurements, pounds and inches are converted to metric before the same formula is applied.
Adult BMI categories
For adults age 20 and older, the CDC lists categories of below 18.5, 18.5 to under 25, 25 to under 30, and 30 or above, with obesity further divided into classes. The calculator uses those thresholds. CDC adult BMI categories.
What BMI can and cannot tell you
BMI is useful for population-level and screening contexts because it is quick and consistent. It does not distinguish muscle from fat, does not measure fat distribution, and should not be used by itself to diagnose health status.
Who should not rely on this adult calculator
This page is not designed for children or teenagers, pregnancy-specific assessment, or clinical decision-making. Athletes with high muscularity and people with unusual body composition may also find BMI less representative.
Use BMI as one part of a broader assessment
BMI is useful for population screening because it standardizes weight for height, but it does not directly measure body fat, muscle mass, fat distribution or metabolic health. Athletes, older adults, pregnant people and some population groups may need additional context. If a BMI result is being used for a health decision rather than general information, combine it with clinical history and measurements chosen by a qualified health professional.