Health 6 min read

Understanding BMI: Ranges, Formulas, and Health Metrics Explained

Learn how Body Mass Index (BMI) is calculated for adults. Understand official WHO BMI classifications, healthy weight ranges, and calculation formulas.

BM Sanjay Samanta & Academic Review Board

Published August 5, 2026

Fact-Checked

Table of Contents

What Is Body Mass Index (BMI)?

Body Mass Index (BMI) is a screening metric that calculates a ratio of an individual’s body weight to their height squared to categorize body mass levels.

BMI Formulas

Metric System: BMI = Weight (kg) ÷ [Height (m)]²
Imperial System: BMI = [Weight (lbs) ÷ (Height (inches))²] × 703

World Health Organization (WHO) Categories

Underweight: BMI < 18.5
Normal / Healthy Weight: BMI 18.5 – 24.9
Overweight: BMI 25.0 – 29.9
Obesity Class I: BMI 30.0 – 34.9

Basic Math Tools STEM Editorial Team Verified

Reviewed by Applied Math Specialists • Editorial Policy

Updated: August 10, 2026

Related Interactive Calculators

Practice Tools

BMI Calculator

Calculate Body Mass Index (BMI = kg/m² or 703·lb/in²), official WHO weight categories, healthy weight ranges, and BMI Prime with interactive visual gauge dials.

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