How to Calculate BMI — Complete Guide

At a glance

What it does and when to use it

BMI compares weight with height and provides a general adult screening measure.

Use it for an initial overview, not as a medical diagnosis.

What to enter

Enter weight and height using one consistent measurement system.

How to read the result

Compare the number with standard ranges while remembering that muscle mass is not measured.

BMI (Body Mass Index) is a simple body measurement calculated from weight and height. It was developed by Belgian statistician Adolphe Quetelet in 1832.

BMI Formula

BMI = weight (kg) ÷ height² (m) Example: 70 ÷ (1.75)² = 70 ÷ 3.0625 = 22.9 Or in imperial: BMI = (weight lbs ÷ height²) × 703

WHO Classification Table

Below 18.5 — Underweight
18.5–24.9 — Normal weight ✅
25–29.9 — Overweight
30–34.9 — Obesity Class I
35–39.9 — Obesity Class II
40+ — Extreme obesity

BMI Limitations

BMI doesn't distinguish between muscle and fat. A muscular athlete may be classified as "overweight" despite excellent health. BMI is a screening tool — not a medical diagnosis.

→ Calculate BMI Now

Common mistakes

Entering centimeters in a field that expects meters.
Treating BMI as an individual medical diagnosis.

Frequently asked questions

Is BMI reliable for athletes?

It may be less useful because it does not separate muscle from fat.

Is one result enough?

No. Trends and personal context matter more than a single number.