How To Calculate Body Fat... The Best and Worst Techniques

What is the single, most effective way to calculate body fat? That's a tough one. It all depends on what on you place most importance on...

Accuracy? Reliability? Cost? Availability? They are all important factors to think about. Fortunately there are quite a few techniques to choose from. Some good, some not so good. We'll take a closer look at each. First up (and the least accurate) is...

Height-Weight Tables

Let's get the least reliable method used to calculate body fat out of the way fist.

Have you ever used height-weight table? Chances are you have...

You look for your height then run your finger across the table until you find the weight that somebody decided, in their great wisdom, was ideal for you. And if you're lucky...

They provide you with body frame sizes as well! So now, if you fall outside the weight range for your height AND your body frame size you get to feel really bad! :-(

Seriously though, height-weight tables are very limited because they simply don't calculate body fat. Most football players for example, are much heavier than the recommendations on height-weight tables. Does that make them unhealthy or overfat?

Of course not. Their large frame size and muscular development contributes to their "excessive" weight. Football players are extreme examples but they highlight the fact that height-weight tables serve little purpose in assessing body composition.

The machines you find in gyms, airports, supermarkets, that ask you to enter your height, age and even...

Your frame size, are just fancy height-weight tables... they don't calculate body fat. And more importantly, height-weight tables will tell you nothing about your general health status. With that in mind let's move swiftly onto...

Body Mass Index (BMI)

BMI is a very simple tool. It's best use is for risk assessment for the general population. Does BMI calculate body fat?

Unfortunately not. Compared to height-weight tables though, it has a much higher association with a person's body fat. How does it work? It's a simple formula...

BMI = Body mass in kilograms (Height x Height in meters) (Divide weight in lbs by 2.2046 to get weight in kg's)

So as an example a 150lb (68kg) woman who is 165cm (1.65m) tall...

BMI = 68 (1.65 x 1.65) 
= 68 2.7 
= 25

This person has a Body Mass Index of 25. What exactly does this mean?

Well there is an association between BMI and many major degenerative diseases. As a person's BMI increases so does their risk of ill health. Have a look at the table below... 

Body Mass Index Classifications
Classification Risk BMI Score
Underweight Moderate less than 18.5
Normal Very low 18.5 - 24.9
Overweight Low 25.0 - 29.9
Obese Class 1 Moderate 30.0 - 34.9
Obese class 2 High 35.0 - 39.9
Extreme obesity Very high greater than 40.0

One important point to remember...

BMI will be inaccurate for many athletes. BMI doesn't calculate body fat so it can't make allowances for muscular development.

Athletes such as bodybuilders, football players, throwing athletes and anyone on a weight training program should avoid using BMI as a way to calculate body fat.

Growing children and very elderly, sedentary adults should also avoid using BMI as a way to calculate body fat.

Along with height-weight tables, BMI has serious limitations. Neither can be used to calculate body fat, unlike the next method...

Girth Measurements

The big advantage of girth measurements is that you need nothing more than a tape measure to calculate body fat. The downsides?

Girth measurements are unsuitable for individuals who appear excessively over or under weight. The technique is also unreliable for athletes who train with weights.

If you don't fall into one of those categories accuracy can still be out by 4% either way. If you calculate body fat to be 20% using girth measurements it actually ranges from 16-24%. Is this a technique worth considering?

Compared to the next 3 coming up... not really. It sounds easy to simply measure girths and it is. But then you have to put the figures into equations and use hard-to-find tables to work out constants and...

It all starts to get a bit complicated. But don't get disheartened just yet. The next 3 techniques are a lot more promising. Introducing...

Skinfold Measurements... The Most Economical Way To Calculate Body Fat?

At last we've come to the first truly reliable technique used to calculate body fat percentage. Along with Body fat scales (more on those in a minute) body fat calipers are just about the most cost effective way to calculate body fat you will come across. Of course that assumes you buy cheap calipers!

So, what are the advantages to using skin fold calipers?

+ Unlike Height-Weight tables and BMI they actually calculate body fat percentage.

+ They are very easy to use. The hardest part is finding the right locations to pinch.

+ They are relatively inexpensive and once you have a set they should last a lifetime.

+They can be used to calculate body fat in the privacy of your own home.

+ They are portable. You can test others in the most convenient place for them.

+ Used correctly they are an accurate and reliable way to calculate body fat.

+ It can be a quick way to calcualte body fat percentages for a large number of people in a short space of time.

Now for the disadvantages...

- For accurate results an experienced examiner is needed... it really is hard to find the precise locations!

- There are different equations used for different people to calculate body fat percentage from skinfolds. Choosing the wrong equation makes a world of difference.

- It is very difficult to test yourself. You may have to ask a friend or family member and this is when skinfold testing becomes unreliable.

- Really cheap calipers won't stay very accurate for long. They aren't as accurate as the more expensive ones to start with.

Don't let these downsides put you off. There is a lot you can do to control the accuracy of skinfold testing. You can even buy a great set of calipers that allow you to test yourself.

Here's more information on how to use skinfold calipers to calculate body fat 

Bioeletrical Impedance Analysis... BIA For Short

Until recently BIA was expensive, difficult to find and required the skills of a highly trained examiner. Not anymore. Body fat scales have appeared on the market and BIA is the technology they use to calculate body fat in seconds.

Their advantages are almost identical to skinfold calipers. As for disadvantages...

- The amount of water in your body, your skin temperature and recent physical activity can all adversely affect the results.

- As with calipers there are different equations used to calculate body fat from your body density. Unfortunately you are stuck with the equation the manufacturers programmed in and it might not be the most one appropriate for you.

Again don't let these put you off. It is probably easier to control the reliability of body fat scales than it is for calipers.

Here's the body fat scales article. It will help you get the most from should you decide to use this method to calculate body fat 

Hydrostatic Weighing... The gold Standard?

If it's accuracy you're after, hydrostatic or underwater weighing is considered the "gold standard". The only way to calculate body fat more accurately is through...

Dissection! Ouch. ;-)

Hydrostatic weighing is also a highly repeatable way to calculate body fat. This simply means that your body composition is the only variable that affects the results. Sounds obvious I know. But factors such as the amount of fluid in your body, different examiners and skin temperature can all adversely affect the results of other tests.

Here's the downside. It can be an expensive, time consuming way to calculate body fat, not to mention difficult to find. A local University may be your best bet. However some larger gyms may have a hydrostatic weighing tank or a Bod Pod (mentioned below).

How does hydrostatic weighing calculate body fat exactly? It is based on Archimede's Principle. The examiner first calculates your body density. How?

By simply measuring the amount of water you displace when you first enter the tank. Then she uses a specific equation to calculate body fat based on your body density.

So to wrap up what's the best way to calculate body fat? Great question!

If your serious about monitoring your health and body fat don't bother with the first 3 techniques -- Height to Weight tables, BMI and girth measurements. Hydrostatic weighing is the most accurate way to calculate body fat if it's an option for you. The best methods to calculate body fat of overall are...

Body fat scales or measuring skinfolds with a set of Skinfold calipers