Man chest being measured

BMI (Body Mass Index) VS Body Fat Percentage

Man chest being measured

Body fat is a very tricky topic: it is tough to monitor and can be hard to calculate.

In fact many people are way off in their approximations of their body fat percentage.

Luckily you are reading this guide which means you are modest, funny and smart. For anyone trying to trim, there are many ways to monitor your progress.

Man chest being measured

Apart from using the weighing scale, you may also measure your BMI (body mass index) or body fat percentage.

But which method is the best? Though most people talk of body fat percentage and BMI interchangeably, they should be used for different purposes or stages in your weight loss journey.

Understanding the two methods will help you monitor your weight loss or fitness progress with clarity and ease. To help you with this, here is a brief primer about body mass index and body fat percentage:

What is BMI (Body Mass Index?)

BMI or Body Mass Index is a simple measure of a person’s weight in relation to his or her height.

Your BMI is not a percentage of your body fat, but just a score that helps ascertain if you are fit.

If you have too much weight for your real height, the difference in weight is usually assumed to be excess fat.

Even though many health care providers claim that body mass index is not an accurate measurement, it is the least expensive and the easiest way to ascertain if your body fat is too high or too low.

Drawing of three different body fat types

Generally a BMI of 25 or higher is considered overweight and you will be at a high a risk of high blood pressure, diabetes, heart disease and other serious illnesses.

What is Body Fat Percentage?

Your body fat percentage is your total fat divided by your weight.

The measurement helps you determine what percentage of your body is fat, what percentage is bone, organs, blood and muscle.

For instance if a person has 15 pounds of fat and weighs 150 pounds, he or she has a body fat percentage of 10 percent.

Body fat percentage not only changes automatically when you lose or gain fat, it also changes when you lose or gain muscle.

In addition, both women and men have different body fat percentages.

For instance a super ripped man can have a body fat percentage of as low as 3 to 4 percent while a super ripped lady can only get to 8 or 9 percent.

Average body fat percentage chart

Image :

The average fat is between 25 and 31 percent for women and 18 to 25 percent for men.

Also note that your fat percentage has nothing to do with your muscle mass.

This typically means that you can have 2 different people with the same fat percentage but look different.

What is the Difference between BMI & Body fat percentage ?

Determining body fat percentage involves more factors than BMI.

It takes into consideration how much of a person’s weight is bone, muscle and fat, while BMI doesn’t.

This means that you can have an appealing BMI, but still carry some weight in your belly which increases your risk of heart disease.

Nonetheless most fat measurement techniques have a margin of error of between 1 to 4 percent and are not easily accessible.

Body Mass Index on the other hand can be used by almost everybody and involves a very simple mathematical calculation.


How to Measure / Calculate your BMI

To determine your Body Mass Index, you or your healthcare provider will need to know your height and weight.

Then take the weight in pounds multiply by 703 and divide by height in inches squared.

Alternatively, you can use the metric method where take the weight in kilograms and then divide by your height in meters squared.

The easy way, you can use an online calculator such as the one available at the National Heart Lung and blood Institute.

You can also find “BMI Tables“, they read very easily, such as this one from wikipedia:

Body Mass Index calculation table

Once you get the number use this table to evaluate your health

-Obese-more than 30

-Overweight-between 25 and 29

-Normal-Between 18.5 and 24.9

-Underweight-less than 18.5

But if you fall into the obese or overweight categories and your weight is okay, you may also want to consider other factors. For example athletes and body builders may have excess weight that is muscle and not fat.

Your ethnicity, diet and age may also affect your BMI.

How to Calculate your Body Fat Percentage

Body fat percentage can be measured in a number of ways:


Calipers pinches your skin lightly in different areas of your body. In women the thigh, hip and triceps are measured.

Man pinching his skin with a caliper

In men the thigh, abdomen and chest are measured. Then based on these measurements, your body fat can be approximated. The method can be difficult to approach, but it is the least expensive.

BIA scales

Smart scales use bio-impedance analyzis to measure your body fat percentage. They run a tiny current between your feet and read various metrics to determine your body fat percentage in just a few seconds.

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We reviewed the best body fat analyzers on this website.

Dexa scan

A highly accurate method. It takes a dual xray of your entire body and gives numbers. You can do this in a medical facility.

Man lying down on a DEXA body fat scanner

There are other methods to measure your body fat percentage, but the most common are the three methods above.

3 thoughts on “BMI (Body Mass Index) VS Body Fat Percentage”

  1. Mike anderson says:

    So basically BMI is made for the “average”, non muscle building guy right ?

    Also i imagine that something like bone density could have a big impact on BMI. Why are people using BMI at all since this seem like a useless metric?

  2. bodyfatgenius says:

    Indeed, BMI is a poor metric to measure your overall fitness. it is still widely used for two main reasons:

    – It’s easy to calculate

    Anyone can calculate Body mass index very easily.

    – It is correlated to body fat percentage in most cases

    Unless you are a confirmed bodybuilder or have a lot of muscle mass, BMI will be correlated to your body fat percentage. It does not mean that it is very accurate, but it gives a close enough idea to use this metric, unless something more specific is required for some reason.

  3. Ryan Gentilcore says:

    BMI sucks. It causes all kinds of body issues without being accurate. I mean, the person who created the BMI formula (a mathematician BTW, not a doctor) explicitly stated that it could not and should not be used to indicate the level of fatness in an individual.

    And for some anecdotal evidence, I submit my own information – I’m 36 years old, 5’9″ and weigh 210. My BMI is 31, or “obese”. My body fat is 17%, which puts me at the top end of the “fit” category.

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