What is BMI? The Complete Guide

BMI Definition

The Body Mass Index (BMI) is a measure that relates a person's weight and height to estimate whether their weight is healthy. It was developed by Belgian mathematician Adolphe Quetelet in 1832 and adopted as an international standard by the WHO in the 1990s.

It is the most widely used nutritional screening tool in the world due to its simplicity: only two data points are needed (weight and height) to obtain an indicator that correlates reasonably well with the percentage of body fat at the population level.

BMI Formula

The formula is very simple:

BMI = Weight (kg) ÷ Height² (m)

Practical example: A person who weighs 70 kg and is 1.75 m tall has a BMI of:

70 ÷ (1.75 × 1.75) = 70 ÷ 3.0625 = 22.9

A BMI of 22.9 is within the normal range (18.5 – 24.9).

What is BMI used for?

• Detect possible weight problems in routine medical check-ups
• Monitor weight evolution over time
• Estimate the risk of weight-related diseases
• Assess the nutritional status of entire populations
• Determine eligibility for certain medical treatments

BMI Limitations

• Does not distinguish between muscle and body fat
• Does not indicate where fat is distributed in the body
• Does not apply equally across all ethnicities
• Requires different interpretation in children, pregnant women, and older adults
• Is a population risk indicator, not an individual diagnosis

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