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Bodyfat Measurement

Whether you are trying a new gainer diet, cutting up, or just curious, it's often a good idea to get a bodyfat measurement done. There are various methods in use, and some are far better than others. In order of decreasing accuracy:

  • Autopsy
    Extremely accurate. The physician seperates your fat from other tissues and weighs everything. Fairly inconvenient, as it requires you to be dead.
  • Hydrostatic Weighing ("Dunk Tank")
    Requires the individual to expel all their air underwater. Expensive and difficult to locate a suitable facility.
  • Skinfold Measurements
    By far the most common method and is generally accurate to within a few percentage points. Cheap (usually about $5 to get the test done at a reputable fitness center). More detail on this method, below.
  • Bioelectrical Impedance (BIA)
    These devices pass a small current between either your hands or feet and determine the effective resistance. From this, and a host of assumptions about the conductivities of various body tissues, they try to determine the percentage of body fat. Some bathroom scales even include this ability but one should be very skeptical of the unit's accuracy. Some people have reported wildly-varying results with these, although some manufacturers claim high correlations with skinfold or underwater weighing results. Very dependant upon your state of hydration.
  • Infra-red (IR)
    Infra-red measurements are made at your finger, and through some magic, they attempt to determine your body fat composition. Very inaccurate, but convenient and fast.
  • Generalized Formulae (waist, height, weight)
    Numerous studies into the anthropometry of various individuals have been compiled into tables that include the person's weight, height, waist and actual bodyfat (generally done via skinfold measurements). A simple linear prediction formula is then created that fits loosely to the average population. These are very easy to use, and cost you nothing, but they should only serve as a very rough estimate. A section below details a few of these formulae.

Skinfold Measurements

A number of formulae have been proposed for bodyfat estimation from sum of skinfolds (SOS), but only two are often used:

  • Durnin & Womersely (DW)
  • Jackson & Pollack (JP)

It seems that the JP equations give slightly more accurate estimates than the DW equations for your average trainer. The JP equations are actually of two varieties, one is a 3-site test, the other a 7-site test. For individuals with low bodyfats, it is best that the 7-site test be used. In general, the locations for the 7 skinfolds are taken as follows:

  • chest
  • axilla
  • triceps
  • subscapular
  • abdominal
  • suprailiac
  • thigh

The actual regression equation for the 7-site JP can probably be found in the British Journal of Nutrition 40:497, 1978. Jackson & Pollack.

It should be noted that although the formulae are available, one should get the actual computation done by a reputable facility (with a computer). There, you should always attempt to get the same person to perform the test, as the results vary significantly from tester to tester. These differences are generally from the exact location of the sites and the way they grab the skinfolds. Thus, with different people making the measurements, you will likely see fluctuations that may not be there.

Your best bet is to get periodic measurements done at a good facility (say, once every 2 months), but then log your own skinfold measurements every 2 weeks. What is important is not the actual bodyfat estimate percentage, rather it is the *change* in skinfold measurements or percentage. If you see a gradual increase in your abdominal skinfold measurement (over time), then you can safely assume that you are putting on fat. Don't measure too frequently, as these measurements could vary enough that the fluctuations due to state of hydration, etc. will outweigh any actual changes in bodyfat.

One should also be aware that it is generally not possible to do these skinfold measurements yourself. Some of them require positioning that would be very difficult (eg. subscapular). So, if you are going to do your own logging of skinfolds, get a friend to do it for you each time. To do it properly, one must use a skinfold caliper, not a ruler, and know how to isolate the fat thickness. There is a specified caliper squeezing force that is used to standardize the measurements (the tester will squeeze the caliper until it 'clicks'), and you will not be able to accurately assess this force with a ruler. Skinfold calipers are expensive, so a ruler may have to suffice (for purposes of general fluctuation estimates).

Generalized Equations

Equation 1:

  • For men: Bodyfat = -98.42 + 4.15*waist - .082*bodyweight
  • For women: Bodyfat = -76.76 + 4.15*waist - 0.082*bodyweight
  • NOTE: "waist" is in inches, "bodyweight" is in pounds.
  • Both formulae will give you the total number of pounds of bodyfat, not your percentage. To get your percentage, divide the result above by your total body weight.

Equation 2:

This method is based on three skinfold measurements. All skinfold measurements should be taken on the right side. Use the following 3 measurements:

  1. Chest: Measure a diagonal fold on the outside of the pectoral muscle, halfway between the nipple and shoulder crease. The fold should be parallel to the outside edge of the pectoral muscle.
  2. Abdomen: Measure a vertical fold one inch to the right of the belly button.
  3. Thigh: Measure a vertical fold at the middle of the front thigh.

Measure when the skin is dry, before exercise, and when you're not overheated. Measure each skinfold 3 times and use the 2 which agree--pinch from the top, measure from the bottom. The standard caliper measures in millimeters, so if yours measures in inches, you'll need to convert the numbers before going on (1 inch=25.4 mm).

Now the math. The sum of these 3 measurements (in mm.) is first used with the person's age to calculate body density in a quadratic equation.

Body Density = (1.1093800 - (0.0008267 * (Sum of 3))) + (0.0000016 * (Sum of 3 * Sum of 3)) - (0.0002574 * (Age))

Percentage Bodyfat is then calculated with the following formula:
% Bodyfat = (((4.95 / Body Density) - 4.50) * 100)

Reference: Practical Assessment of Body Composition, A. S. Jackson and M.L. Pollack. The Physician & Sports Medicine, Vol. 13, No. 5, May 1985.

Equation 3:

Thanks to m.f.w. post from Jeff Amason (stronguy@ix.netcom.com):

The equation I use is from Parillo's Bodystat Maunal. I use Slim Guide calipers and do a 9 point measurement:

  • Upper pec (horizontal fold)
  • Subscapular (vertical fold)
  • Bicep (vertical fold)
  • Inside tricep (horizontal fold)
  • Kidney (horizontal fold)
  • Suprailliac (horizontal fold)
  • Abdominals (vertical fold)
  • Mid quad (vertical fold)
  • Inside calf (vertical fold)

Total all measurements and divide by your body weight. Multiply this total by 0.27. This will be your % body fat.

 


Reader's Comments:

Please leave your comments or suggestions below!
2017-03-23jane nyabuti
 good information. very educative
2011-10-05Rachel
 Which is a better method to use: 7-site or 3-site?
 Generally the 7-site should provide more accurate estimates.
2010-06-20Victor Migiro
 happy with the studies you've done. wish to request for information on MUAC reference standards and cut off points. computation of nutritional status using skinfolds and dietary assessment and estimation and interpretation of percentage body fat. thanks.
2008-04-28pam
 I enjoyed your response to the bodyfat percentages for men (question you gave Jim on 1/28). Can you explain the same for women as well?
 The same reference suggests that the average bodyfat percentage for women is around 22-25%, with a safe / healthy minimum of 12%.
2007-03-12Darcy
 I'm happy that this site is in laymans terms. All the other sites either calculated it for you, or were from a medical journal and were too difficault to understand. I run my own business and need this info to measure my client's body fat. Thanks for the plain english.
2007-03-11lo
 I've recently took a skin fold test for a job offer. I needed to be at or under 22% body fat I was at 25% though. I felt that day as if I were retaining water that day. My question is does retaining water make a differance in the measuments? If so do you recommend I cut water to be tighter the next time I go and get a skin fold test.
 
2007-02-12cannes
 Hi, i am on doing my research about obesity in pregnancy, would you mind giving me some information about skinfold measurement for pregnant women, and the body fat ranges classification to determine obesity ?
Thank you very much for the information..
2006-08-27ivan
 please give me the proper procedure in doing skinfold measurement.. pls send it to me ASAP!
2006-05-04Joe
 Hi. I have an interesting situation going. I am very lean, my body fat is 7%, and when I stand up I have a six pack (I'm not exaggerating), but when I sit down, I have fat rolls pouring over my belt. Do I have to get even leaner to get that to go away? I could post you pics of me both standing and sitting to show you what I mean if you gave me your email.
 Everyone has a slightly different distribution of fat across their body. Yours might be clustered around your lower abdominals. If it bothers you, the most likely solution would be to try leaning up a little more, within reason. I can't think of much else that would help out -- anyone?
2006-03-01Mike
 Is constant for women different than men when doing the Parillo's Bodystat (9 point skinfold test)? I heard that women's constant was .30 as opposed to men's .27.
2006-01-28Jim
 Thanx, I got 12%... do you know where i can get a guide to tell me what that means? is it good? is it fat? Cheers.
 12% is very good for a guy, not ripped, but healthy. The average male adult bodyfat is around 15-18% [Reference]. For male athletes, a target range is 6-13% [Reference]
2006-01-28Jim
 Thanx, I got 12%... do you know where i can get a guide to tell me what that means? is it good? is it fat? Cheers.
2006-01-26ali alshamli
 thank you very much about your web site

would you send me the validity and relibility of the second equation and a copy from the above article or the pages of the book
thanks alot
 I am not certain of the reliability of the 7-point JP equation, but my understanding is that it has one of the better correlations with the real bodyfat measurements.

There are more details regarding the use of the test and related references here.
2006-01-15jamal
 i actually will like to say that use done a very good work in this website, but i would like to see which one jp and dw is more accurate and evidence to back that up.

thanks
jamal
 There are a few studies that have shown the correlation between the sum of skinfold formula-based tests and the hydrostatic weighing which is the most realistic measure. Jackson-Pollock's study indicated issues with how differences in body density and demographics affected their quality of correlation. One interesting page I have seen on this topic is here.

 


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