What Is BMI and What Does Your BMI Number Mean?

What does BMI stand for?

BMI stands for Body Mass Index. It is a simple calculation that compares an adult’s weight with their height to produce a single number.

BMI is widely used as a screening measure because it is quick and easy to calculate, but it does not directly measure body fat or diagnose health.

Want to try the idea yourself? Use the BMI Calculator.

How is BMI calculated?

Using metric units, BMI equals weight in kilograms divided by height in metres squared. Someone weighing 70 kg at 1.75 m has a BMI of about 22.9.

With imperial measurements, the formula uses pounds and inches with a conversion factor. The BMI Calculator handles either unit system automatically.

What do BMI ranges mean?

Common adult categories describe BMI below 18.5 as underweight, 18.5 to 24.9 as a healthy-weight range, 25 to 29.9 as overweight and 30 or above as obesity.

These are broad population screening ranges. They should not be treated as a complete assessment of an individual person.

Where BMI can be misleading

BMI cannot distinguish muscle from fat. A muscular athlete can have a high BMI despite relatively low body fat, while two people with the same BMI can have very different body composition.

Age, pregnancy, ethnicity and some medical circumstances can also affect how useful standard BMI categories are. Children use age- and sex-specific growth measures rather than the standard adult categories.

How to use your BMI result

Use the BMI Calculator for a quick estimate and treat the result as one piece of information rather than a verdict on health.

If weight or health is a concern, a healthcare professional can consider BMI alongside factors such as waist measurement, medical history, blood pressure and other relevant information.