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Body Fat Calculators

Obesity occurs when the body stores excess body fat.

Body Fat Percentage

The normal body fat percentage for men is about 15 to 20% by weight, and the normal range for women is 25 to 30%.

Although there are some differences, many experts define obesity as body fat percentage (BF%) greater than 25% in men and greater than 33% in women.

Body fat percentage is rarely used, however, to define obesity, instead the body mass index (or BMI) is used more commonly.

Although in the past researchers have stated that body mass index and body fat are closely correlated, recent studies suggest that the BMI is a poor estimate of the degree of body fat.

One study by the Mayo Clinic College of Medicine, suggested that BMI is limited at diagnosing obesity, particularly for “individuals in the intermediate BMI ranges, in men and in the elderly“.

They found that a cut off point of 30 had good specificity (ie those above a BMI of 30 were almost all obese), but missed more than half of people with excess fat.

BMI results on 13,601 individuals suggested that 19.1% of men and 24.7% of women were obese, but the body fat percentage measurements indicated that obesity was present in 43.9% of men and 52.3% of women.

Body Fat Calculators

The body fat percentage has been estimated by using a number of calculators over the years. A summary of the most popular ones found on websites is given.

The Deurenberg equation has been used to correlate BMI with BF% as follows:

body fat percentage = (1.2 x BMI) + (0.23 x age) – (10.8 x sex) - 5.4

where age is in years and sex is 1 for male and 0 for female. This equation has a standard error of 4% and accounts for approximately 80% of the variation in body fat.

Other calculators are based on anthropomorphic measures (tape measurements taken around various parts of the body).

The YMCA calculator is based upon body weight in pounds, and waist in inches (at the navel), to calculate body fat percentage using the formulas:

For women:

BF% = [4.15 x (waist in inches)] – [0.082 x (weight in pounds)] – 76.76

So, for a woman with a 33ins waist, weighing 140lb, her body fat % would be:

= [4.15 x 33] – [0.082 x 140] – 76.76

= 136.95 – 11.48 – 76.76

= 48.71

For Men:

BF% = [4.15 x (waist in inches)] – [0.082 x (weight in pounds)] – 98.42

So, for a man with a 35ins waist, weighing 180lb, his body fat % would be:

= [4.15 x 35] – [0.082 x 180] – 98.42

= 145.25 – 14.76 – 98.42

= 32.07

The other popular anthropomorphic calculator is that developed by the US Navy.

The Navy calculator:

The Navy refer to their method as ‘rope and choke’ technique; they claim it is as accurate as some of the caliper methods, but simpler to carry out. Here’s how you do it:

Measure your height barefoot.

Measure your waistline (at the naval for men; at the narrowest point for women).

Measure the neck, allowing the tape to slope slightly down below the voicebox.

Women only: measure the hips at the largest level.

The calculator in inches for men:

BF% = [86.010 x log10{(abdomen) - (neck)}] – [70.041 x log10(height)]+36.76

The calculator in inches for women:

BF% = [163.205 x log10{(abdomen)+(hip)-(neck)}] – [97.684 x log10(height)] - 78.387

Bottom Line

Typically, these calculators give wildly differing results. They are fun to play about with, but do not expect any degree of consistency between them.

Ideally, if you are going to estimate your body fat with one of these calculators, use one calculator only, stick with it and just use the initial record as a baseline indication of where you are now.

At Slimmer Secrets we never measure body fat. The drop in weight from following the success principles encouraged by Slimmer Secrets will guarantee reduced levels of body fat which in turn improve the quality of your health and your life.


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