How To Calculate Body Fat

What is the single, most effective way to calculate body fat? There are many techniques out there to choose from, but what is the msot effective?

Let's start with the LEAST reliable method and yet the most common method used.

Weight to Height Ratio. Weight/Height tables are very limited because they simply don't calculate body fat. If you have two people who are 5'10 and weigh 200lbs, one is a body builder and has little fat on their body and the other is very obese. The weight/height table will say they are both overweight and at risk.

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 and they don't calculate body fat. And more importantly, height-weight tables will tell you nothing about your general health status.

BMI (Body Mass Index) 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.

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

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.

Girth Measurements such as waist to hip ratio or waist to height ratio is a better way to measure body fat, but not if you are severely overweight or under weight. 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? If you are on a limited income, then of the 3 we just mentioned, this would be the best, but not the most effective.

Skinfold measurements will do much better at determining body fat. The problem is you need an experienced person to do the measurements for you, it is really challenging to do them on your own as finding the right place to pinch is a challenge. So this is a much better method than the above, but you will need to put out some money for a good pair of calipers (cheap ones will fail you) and an experienced technician to give you accurate results.

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, but the disadvantages are that the amount of water in your body, your skin temperature and recent physical activity can greatly affect the results. There are also different equations used to calculate body fat based on your body density. You are stuck with whichever equation the scale manufacturer programmed in and it might not be ideal for you.

Hydrostatic Weighing

And we have a winner! 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 affect the results of other tests.

It can be an expensive, time consuming way to calculate body fat, not to mention difficult to find. A local University or some gyms may have a hydrostatic weighing tank or a Bod Pod.

How does hydrostatic weighing calculate body fat exactly? It is based on Archimede's Principle. The examiner first calculates your body density by simply measuring the amount of water you displace when you first enter the tank. Then they use a specific equation to calculate body fat based on your body density.

This is really the best possible way to determine your body fat. If this is not an option for you, then go with skinfold calipers or body fat scales.