Body Mass Index

The Body Mass Index (BMI)

"When am I too heavy and how much excess weight do I have?" The current scientific standard answers this question using the BMI. BMI stands for Body Mass Index. Your weight and height are used to calculate a number, which is then interpreted. The formula is

BMI =	Body weight in kg

	(Height in m)²

Example for 1.75 m height and 70 kg weight:

BMI =	70	= 22.86

	(1.75)²

BMI calculator

The calculation isn't something you can easily do in your head. It's easier with a BMI calculator. Just enter your weight and your height and read off your Body Mass Index. You can also move the BMI slider to see what weight you'd need for a target BMI. As a nice touch, a 3D computer figure illustrates the calculated Body Mass Index.

Meaning of BMI (Body Mass Index) according to WHO

BMI value	Meaning
under 19	Underweight
19 to 25	Normal weight
25 to 30	Overweight
30 to 35	Obesity (Class I)
35 to 40	Obesity (Class II)
over 40	Obesity (Class III)

What to know

The formula for BMI comes from the Belgian mathematician Adolphe Quetelet in the 19th century. In medical research it is very practical to reduce weight status to a single number, which is why BMI has become widely used.
The calculation of the Body Mass Index is the same for everyone. It does not distinguish by age or sex. Children have their own assessments in that case sex is also taken into account. You can find a table here: www.bmi3d.de/kind.html. The WHO (World Health Organization) classification applies to all adults. This is often criticized, because many studies show that a slightly higher BMI can be medically reasonable as people get older. The U.S. National Research Council (NRC) already presented a table in 1989 where, for example, a BMI of 24 to 29 is considered normal from age 65. However, such a complicated classification makes the use of BMI in medical research more difficult, which is why it is not used. BMI is only a rough guideline, because it does not take into account body build and sex or the individual composition of body mass into fat and muscle.

You can also easily calculate the Body Mass Index with a simple calculator if you know how. Here's the trick:

	Steps:	Example:
1.	Enter your weight in kilograms	70
2.	/ (divided by)	/
3.	Enter your height in meters	1.75
4.	/ (divided by)	/
5.	Enter your height in meters	1.75
6.	=	=
		22.86

Weight and blood pressure

Overweight has a major effect on blood pressure. In about every second patient, blood pressure falls when weight is lost. You can expect a reduction of 5 to 20 mmHg for every 10 kg of weight loss. Since overweight or obesity together with high blood pressure is one of the four major risk factors (along with smoking and high cholesterol) for cardiovascular disease, it makes extra sense to tackle excess weight or obesity.

Criticism of BMI

If you accept no criteria other than BMI, it can, however, become costly. Health insurance companies assess your risk of illness based on your BMI. Someone who is very athletic, for example, can have a high BMI for their height, because BMI is calculated only from weight and height and ignores the distribution of muscle, water and fat in the body.

An American study also found that about 8 percent of people with a normal BMI still have an unhealthy metabolism.

Sources

This article comes from BloodPressureDB – the leading app since 2011 that helps hundreds of thousands monitor their blood pressure every day. Our content is based on carefully researched, evidence-based data and is continuously updated (as of 12/2025).

Author Sabine Croci is a qualified medical assistant with many years of experience in internal medicine and cardiology practices as well as in outpatient care, and has led BloodPressureDB's specialist editorial team since 2015. Thanks to her extensive additional qualifications as a paramedic, first responder and in various therapy and emergency areas, she provides solid, practical and reliably reviewed information.