All about body fat percentages

What is body fat percentage?

One of the jobs of a Personal Trainer is to understand your body composition, what your unique body is made up of, and then to help you reach your goals; this may be fat loss, inch loss, strength or muscle gain; it’s all down to the individual. Part of your body composition is your body fat percentage which is simply the part of your body that is made up of fat. Our bodies need fat to function properly but the key is to understand how much fat is healthy

How is it calculated?

There are many ways of calculating your exact body composition such as a CT scan which produces radiographic images of the body showing different types of tissue; these include water, fat, bone and muscle. The most well-known methods of measuring body composition are:

The Hydrostatic Technique

This is underwater weighing and is considered the reference standard for assessing body composition. Bone and muscle tissues are denser than water and fat is less dense so the person is weighed on land and then lowered into the water and weighed underwater, therefore, someone with a lower percentage of body fat weighs more underwater than on dry land. Even though this is the standard it isn’t available to most PTs so it’s unlikely you’ll get your body fat percentage measured this way.

Anthropometric Techniques

This technique is much more accessible to PTs. This involves measuring the size and proportion of your body using a tape measure or skinfold callipers. These measurements can then be used to calculate the person’s body composition. This is probably the most common method as it’s quick and easy and you can do it anywhere (as long as it’s somewhere pretty private!)


Some scales measure body fat percentages by passing a very low electric signal through your body which can’t be felt. As with hydrostatic weighing bone and muscle is denser than fat so the signal slows down when passing through bone and muscle. This can give a fairly accurate indication of body fat percentages.

Why is it important to know what my body fat percentage is?

Your body needs fat to function so it’s important to see whether you have the correct levels of fat within your body. Too much and you are at greater risk of some obesity-related diseases such as diabetes, high blood-pressure and some forms of cancer. Too little and your well-being and reproductive system can be effected and also your organs can lose the ability to absorb vitamins effectively.

If your goal is to lose fat then using your body fat percentage as a baseline is a great indicator of how well you are doing. Muscle weighs more than fat so if you are on an exercise programme that involves resistance training (weights) then it’s highly likely that the number on the scales will increase even as your size decreases because it’s the fat that you’re burning off. This is why obsessing over how much you weigh can be dangerous and why you should not go just by weight alone, but by fat percentage and by your measurements.

What does my percentage mean?

According to the American College of Sports Medicine, the benchmark of Personal Training guidelines;

“For males and females, essential fat values are typically considered to be 3% and 12%, respectively. Fat above the minimal amount is referred to as nonessential fat. It is generally accepted that a range of 10-22 percent for men and 20-32 percent for women is considered satisfactory for good health.”

Some tables break this down even further into age categories:

Males Not recommended Low Mid Upper Obesity
18-34 years <8% 8% 13% 22% >22%
35-55 years <10% 10% 18% 25% >25%
55+ years <10% 10% 16% 23% >23%
Females Not recommended Low Mid Upper Obesity
18-34 years <20% 20% 28% 35% >35%
35-55 years <25% 25% 32% 38% >38%
55+ years <25% 25% 30% 35% >35%


So if we use this table we can see that a female aged 32 should try to maintain a body fat percentage of between 20-35% – ideally in the lower end of that range at 20-28%.

This table is slightly clearer as it classifies body fat percentage into underfat, healthy, overfat and obese:

Image: Body Fat Chart

If we use this table we can see that for our 32 year old female to be ‘healthy’ the ideal is 21-33%. And we don’t reach the horrible ‘obese’ word until 39%.

In both tables you can see that women’s ‘healthy’ ranges of body fat is higher than men’s this is because women need more fat to function properly.

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