How to calculate BMI step by step

The BMI uses your weight (in kg or pounds) and your height (in meters or inches) to give you a calculation that provides you a measure of your body fat. The formula for how to calculate BMI was devised in the 1830s by Belgian mathematician Adolphe Quetelet and is universally expressed in kg/m2.

calculate BMI


How to Calculate BMI

Body mass index is a measure of body fat and is commonly used within the health industry to determine whether your weight is healthy. BMI applies to both adult men and women and is the calculation of body weight concerning height. This article delves into the BMI formula and demonstrates how you can use it to calculate your own BMI.

The first formula we’ve listed is the metric BMI formula, using kilograms and meters. The second one is the imperial BMI formula, which uses units of pounds and inches. Converters are available for kilos to stonekilos to pounds and ounces and pounds, should you need them.

Metric BMI Formula

BMI = weight (kg) / [height (m)]2

Imperial BMI Formula

BMI = 703 × weight (lbs) / [height (in)]2

Using the BMI formula (metric units)

  1. Multiply your height in meters (m) by itself
  2. Divide your weight in kilograms (kg) by your step 1 result

Using the imperial BMI formula

  1. Multiply your height in inches (in) by itself
  2. Divide your weight in pounds (lbs) by your step 1 result
  3. Multiply the result from step 2 by 703.

BMI Categorization

The BMI statistical categories below are based on BMI scores and apply to adults age 20 years and upwards. The World Health Organisation (WHO) regards a healthy adult BMI to be between 18.5 and 25.

BMI BMI Category
Less than 15 Very severely underweight
Between 15 and 16 Severely underweight
Between 16 and 18.5 Underweight
Between 18.5 and 25 Normal (healthy weight)
Between 25 and 30 Overweight
Between 30 and 35 Moderately obese
Between 35 and 40 Severely obese
Over 40 Very severely obese



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