How to Calculate Body Mass Index (BMI)

BMI is a simple calculation using height and weight to screen for weight categories. It is widely used by healthcare providers as an initial assessment tool.

The Formula

BMI = Weight (kg) / Height (m)^2

Where:

BMIBody Mass Index — Weight-to-height ratio classification number
WWeight — Body weight in kilograms
HHeight — Height in meters

Step-by-Step Example

Here's how to calculate body mass index (bmi) step by step:

  1. 1Measure weight: Weigh yourself in kilograms (or convert from pounds by dividing by 2.205).
  2. 2Measure height: Measure your height in meters (or convert from inches by multiplying by 0.0254).
  3. 3Square height: Multiply your height in meters by itself.
  4. 4Divide: Divide your weight by the squared height to get your BMI.

Following these 4 steps gives you the final body mass index (bmi) value.

Skip the Math

A person weighing 70 kg at 1.75 m tall has a BMI of 70 / (1.75)^2 = 22.9, which falls in the normal range.

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Why You Need This Calculation

  • BMI provides a quick screening tool to identify potential weight-related health risks.

Common Mistakes

Mixing up metric and imperial units.

Convert all measurements to the same system before calculating.

Treating BMI as a definitive health diagnosis.

BMI does not account for muscle mass, age, or body composition.

Using adult BMI charts for children.

Children require age- and sex-specific BMI percentile charts.

Frequently Asked Questions