How to Calculate BMI: Formula, Categories & Health Guide

Body Mass Index (BMI) is a widely used clinical screening tool that evaluates whether an individual has a healthy body weight relative to their height. Health organizations globally use BMI as a quick method to identify weight categories such as underweight, normal weight, overweight, and obesity.

While BMI does not measure body fat directly, it provides a reliable initial baseline for adults. This guide explains how BMI is calculated, breaks down the mathematical formula for both metric and imperial units, outlines official World Health Organization (WHO) categories, and shows how to check your score using the CalculatorAll BMI Calculator.

Quick Answer

To calculate your BMI using metric units (kilograms and meters):

BMI = Weight in kg / (Height in meters)²

For example, an adult weighing 70 kg with a height of 175 cm (1.75 meters):

BMI = 70 / (1.75 × 1.75) = 70 / 3.0625 = 22.86

A BMI of 22.9 falls squarely within the Healthy / Normal Weight range (18.5 – 24.9).

Official World Health Organization (WHO) BMI Categories

Once your BMI value is calculated, compare it against established health ranges:

The Metric & Imperial BMI Formulas

1. Metric Formula (Kilograms & Meters)

BMI = Weight (kg) / (Height (m) × Height (m))

2. Imperial Formula (Pounds & Inches)

BMI = [Weight (lbs) / (Height (in) × Height (in))] × 703

Step-by-Step Numerical Example

Let's calculate BMI step-by-step for a metric scenario:

• Weight: 70 kg
• Height: 175 cm

Step 1: Convert Height from Centimeters to Meters

Height in meters = 175 / 100 = 1.75 m

Step 2: Square the Height Value

Height² = 1.75 × 1.75 = 3.0625 m²

Step 3: Divide Weight by Squared Height

BMI = 70 / 3.0625 = 22.857 ≈ 22.9

How to Calculate BMI Using CalculatorAll

Instead of doing decimal conversions and squaring height manually, enter your details into the CalculatorAll BMI Calculator.

1. Select Units: Choose Metric (kg/cm) or Imperial (lbs/in).
2. Input Weight & Height: Enter your current measurements.
3. Click Calculate: Get your exact numerical BMI score instantly.
4. View Health Range: Compare your score against target clinical boundaries.

Limitations of BMI

While BMI is useful for general screening, it has key limitations:

• Muscle vs. Fat: High-performance athletes and bodybuilders may register a high BMI due to dense muscle mass rather than excess body fat.
• Age and Gender Differences: Older adults naturally lose lean muscle mass, which BMI does not differentiate.
• Fat Distribution: BMI does not account for visceral abdominal fat.

Frequently Asked Questions

What is a healthy BMI for adults?

A BMI between 18.5 and 24.9 is considered normal or healthy for adult men and women according to international WHO guidelines.

Does BMI apply to children and teens?

No. Children and teenagers are evaluated using age-and-gender-adjusted BMI percentiles rather than adult cutoff ranges.