BMI Guide
An in-depth adult BMI guide explaining the formula, screening categories, limits, and interpretation.
What BMI measures
Body mass index is a ratio of weight to the square of height. It provides a quick standardized screening indicator across adult populations. It does not directly measure body fat, fitness, blood pressure, blood sugar, or overall health. A BMI number is one piece of context, not a diagnosis.
Interpreting the standard categories
For adults 20 and older, the usual reference categories are under 18.5, 18.5–24.9, 25–29.9, and 30 or higher. These cutoffs are broad screening thresholds. They should not be treated as a complete health assessment or universal personal targets.
Why the same BMI can mean different things
Two people with the same height and weight can have different amounts of muscle, body fat, and different fat distribution. BMI does not reflect those differences. Individual medical history, body composition, waist measurements, and other clinical indicators can matter.
Using a BMI result responsibly
Confirm that height and weight are entered correctly. Consider the measurement trend rather than a single isolated reading. If your result concerns you, discuss it with a qualified clinician who can consider your circumstances. Avoid making treatment or diet decisions based only on BMI.
When this calculator is not suitable
This calculator uses adult categories and is not intended for children or teenagers. Pregnancy and certain medical circumstances require specialized interpretation. It is not a diagnostic or treatment tool.
Further reading
The methodology page describes the exact formula and rounding. The examples page demonstrates common calculations. For general guidance see the CDC adult BMI information.