3 ways to measure body fat - Why body fat matters

The Running Bug team check out three ways to measure body fat and composition, from economy measures to 'high-tech', top end, and explain why it matters.

3 ways to measure body fat - Why body fat matters

Body composition

Describes the different compartments that make up a person’s overall weight, including:

  • Lean mass
  • Fat mass
  • Body water
  • Bone mass

Body fat

The one we’re most concerned about is fat mass. A healthy fat mass range for fitness is 21 to 24 per cent for females and 14 to 17 per cent for males. Athletes can expect to range between 14 and 20 percent for females, 6 to 13 percent for males, and the average bod, 25 to 31 percent female and 18 to 24 percent male.

Why fat percentage matters for runners

Running performance

Excess fat stores leave athletes lugging extra weight around, reducing speed, and affecting the body’s ability to thermo-regulate (i.e. dissipate heat).

Weight loss

We often put too much emphasis on weight, it’s vital to monitor body composition as changes in body mass do not necessarily reflect changes in body fat levels. Lean muscle mass means you’re packing more power, and you won’t necessarily shed lots of pounds.

Check out this article explaining how to burn fat and build muscle and don't miss these quick and easy tips to help you burn fat.

3 ways to measure your body fat

ECONOMY: Skinfold callipers

The skinfold calliper is a device that measures the thickness of a fold of your skin with its underlying layer of fat. You can use it to measure fat in key areas, the waist, biceps and triceps, below the scapula (shoulder blade). Once added up, a simple calculation will give you your body fat percentage.

Pros: Quick, cheap, simple – easy to repeat.

Cons: The technical skill of the tester will be a big influence on your results.


Bio Electrical Impedance Analysis (BIA) describes small alternating currents flow through the body. Because the body is made up of a high percentage of water containing electrolytes it’s a great conductor for the current. Fat contains very little water and is therefore a poor conductor. The resistance to the flow is calculated to measure fat mass. BIA is the method that is used by most weighing scales that measure body fat.

Pros: Quick and easy, and relatively inexpensive. Tanita and Garmin have linked up so that you can upload data onto Garmin Connect and measure your fat as well as your mileage.

Cons: Isn’t always accurate as it’s affected by what you’ve eaten and drunk.

TOP END: Water, air and radiation

At the top end, methods employed by sports scientists to measure body fat include hydrostatic measurement (bone and muscle mass is more dense than fat mass, so the less fat you have the heavier you are in water, the more fat you have the lighter you will be). To measure more components of body composition you can also try Dual-Energy X-ray Absorptiometry (DEXA), originally used for measuring bone density, it uses low level radiation and a body scanner to establish lean mass, fat mass and mineral mass.

Sian Desmond from the Running Bug tried out the latest high-tech method, the Ki Bod Pod, from the makers of the Ki Fit. The Ki Performance Bod Pod uses changes in air pressure to determine your body composition, not just fat mass.


“I was told to wear tight clothes, not eat for two hours, and avoid wearing any metal (bra straps etc). The test itself is very straightforward and only takes three minutes. I stepped into the pod and took a seat. The door was shut and a friendly voice told me to sit still, relax and breathe normally. There were a couple of clicks and the door was opened and closed, another couple of clicks and once again the door was opened and closed for the third and final measurement. That was it – test was over.

“I had been warned beforehand that my ears may pop from the pressure but, I didn’t feel a thing. It was a bit strange looking out of the window. I felt a bit like Mork in his spaceship.

“The method of measurement is similar to that used in underwater weighing. Using air displacement, the changes in pressure determine body density (mass/volume). A special calculation is then used to measure fat mass (%), lean mass (%), fat mass (kg), lean mass (kg), and body mass (kg).

“I was also measured at key body circumference points, my waist, hips, upper thigh, mid-thigh and upper arm, which gave me a detailed analysis of how to spot and reduce fat from these areas.

“The results, plus graphic representations of my fat’s distribution were sent to me in a detailed report by email within 24 hours of the test – with an action plan on how to shift the fat, including diet and exercise tips. For anyone serious about weight loss, and needing motivation to run, this is well worth the £100 investment.”

Sian had her Ki Bod Pod assessment at Urban Retreat, Harrods, London.

Pros: Accurate, quick, easy and holistic approach.

Cons: Expensive.

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