Bodyfat Analysis Weights - Pepsi Bottles and Pennies

This set of weights is extremely close to as accurate as the concrete-filled PVC Baton set. It has the value of being very simply and quickly made, and of essentially only costing you about $2 total for the label set that goes on each Baton! I don't know how indestructible they will be, but empty Pepsi bottles seem to last forever in landfills, and everyone has dropped a Pepsi bottle at one time or another and they never seem to crack!

As with the other Baton sets, you would only need to hold a maximum of two of these Pepsi Batons.

This approach should provide an accuracy of around 1% or better regarding the bodyfat percentages. If you intend to regularly measure your bodyfat percentage (every week or every month), and you do not want to go to a YMCA or Health Club and have a swimming pool or (freshwater) lake, this might be a logical choice. The excellent accuracy (and repeatability) can give better feedback about your success in your Progress Chart!

If you have your own swimming pool, your friends, relatives and neighbors will certainly want to learn their bodyfat, so you might as well make all 26 of them (Batons A through X and the float and FLOAT)! This particular approach is so simple and fast to make that you might even decide to make the 23 extra Batons that combine float with a Baton.

It is our hope that enough YMCAs and Health Clubs near you will have the precision (calibrated) set of PVC bodyfat batons and that they will offer either a free service or a nominal ($1) charge to test bodyfat analysis, such that few people would see reason to need to make their own!

There appear to be around 17,000 membership-based Health Clubs in the USA. There are also many other non-membership-based facilities that have swimming pools. That includes around 29,650 Public High Schools, 6010 Private High Schools, 7,000 Post-Secondary Schools which have swimming pools. There are also many thousands of (summer) outdoor Municipal Swimming Pools. So we think that there are at least around 74,000 public swimming pools which might choose to provide this service for their communities! Our hope is that one of these pools is near to nearly every American and that they each make or get their own set of these Batons, so that everyone would have the chance to use a publicly-available set of this system for no more than a dollar cost.

To make this set of Batons, you first need to save up several dozen 20 ounce empty plastic Pepsi bottles AND THEIR CAPS. You might want to go to a bank and withdraw around $120 in rolls of pennies, mostly so you could trust that a roll contains exactly 50 pennies! This expenditure is not actually a cost, as they remain pennies / money, and at any time you stopped using the Batons, you could take the pennies back to the Bank to get your $120 back!

The Pepsi bottles need to be empty of any Pepsi, and there seems some value in filling them with water and then emptying them just to get rid of some stickiness that seems to sometimes endure! The bottles should then be turned upside down so any water empties out. The Pepsi labels are easily removed.

As an example, we can take one dry 20 ounce Pepsi bottle and put a large A label on its side. Then drop five rolls of pennies into it, which is 250 pennies as long as the Bank was accurate. You can see from the chart below that you need to add 22 additional pennies to have 272 inside it. Securely screw on the top and you are done with that one!

Try to get relatively NEW pennies. Pennies that get worn have some metal worn off and they are not as heavy. Also, ACTUAL COPPER pennies were much heavier than the modern pennies that are 97.5% Zinc, so that could affect the accuracy. We have provided the actual final weights of each Pepsi Baton (and Pepsi Float) in grams, so if you have an accurate metric scale, you could ensure extreme accuracy. In THAT case, you could actually fill many of the Pepsi bottles with sand or nearly anything else that does not change over time! However, sand is not dense enough to fit enough (dry) sand into the Batons for I and above, so you would need to use the pennies or some other more dense material in those.

You can see that you can assemble the entire set of Batons very quickly. There will be NO cost for the discarded Pepsi bottles, maybe $2 cost for the sheet of stick-on labels, and no actual cost for the pennies. Not bad, a total of $2 cost! Of course, if neighbors and children visiting your pool realize that there is more than $6 of pennies in some of the Batons, they might occasionally disappear! We don't see that as our problem!

We encourage GLUING on the caps so that kids do not open them up and change the calibrated weight by dumping anything out or adding anything in!

Empty Plastic 20 ounce Pepsi bottles with some pennies in them Letter Actual Total Weight
272 pennies insideA705 grams
290 pennies insideB751 grams
308 pennies insideC796 grams
326 pennies insideD842 grams
345 pennies insideE887 grams
363 pennies insideF933 grams
381 pennies insideG978 grams
399 pennies insideH1024 grams
417 pennies insideI1069 grams
435 pennies insideJ1115 grams
454 pennies insideK1160 grams
472 pennies insideL1206 grams
490 pennies insideM1251 grams
508 pennies insideN1297 grams
526 pennies insideO1342 grams
544 pennies insideP1388 grams
562 pennies insideQ1433 grams
581 pennies insideR1479 grams
599 pennies insideS1524 grams
617 pennies insideT1570 grams
635 pennies insideU1615 grams
653 pennies insideV1661 grams
671 pennies insideW1706 grams
690 pennies insideX1752 grams

Precision floats, for people who naturally sink
an empty one-liter Pepsi bottle with capfloat
an empty two-liter Pepsi bottle with capFLOAT
The one-liter and two-liter Pepsi bottles are a little bit heavy for our needs but this float only introduces an error of around 1/2 of one letter in this system. The FLOAT is farther off in being too heavy by about 3.5 letters. In other words, the float is fine for anything short of actual Laboratory accuracy! If you need to use the FLOAT it might pay to build the FLOAT for the PVC set of Batons which would be accurate. There is no obvious way to increase the flotation of these two Pepsi bottles short of trying to fill them with Helium or Hydrogen gas! And even that would not have a large enough effect!

The float and FLOAT functions can also be handled as a SINGLE Baton, combining the effects of both a Baton and a Float, involving an empty Pepsi bottle and some pennies. The middle column below gives the Designation of the TWO separate Batons (float and a Baton) that is used in the other Baton sets (to reduce the total number of these things that need to be lying around!). So if you use the third one below, which is designated float + B, it would only be a single Baton but to use the automated Calculator, you would have to click on BOTH the float button AND the B button.

The first 11 Batons below use the Liter or 1000 ml size of the Pepsi bottle.
NO pennies insidefloat alone50 grams
12 pennies insidefloat + A79 grams
30 pennies insidefloat + B125 grams
48 pennies insidefloat + C170 grams
67 pennies insidefloat + D216 grams
85 pennies insidefloat + E261 grams
103 pennies insidefloat + F307 grams
121 pennies insidefloat + G352 grams
139 pennies insidefloat + H398 grams
157 pennies insidefloat + I443 grams
176 pennies insidefloat + J489 grams
The Batons below use the 20 ounce size of the Pepsi bottle.
17 pennies insidefloat + K70 grams
35 pennies insidefloat + L116 grams
53 pennies insidefloat + M161 grams
71 pennies insidefloat + N207 grams
89 pennies insidefloat + O252 grams
108 pennies insidefloat + P298 grams
126 pennies insidefloat + Q343 grams
144 pennies insidefloat + R389 grams
162 pennies insidefloat + S434 grams
180 pennies insidefloat + T480 grams
198 pennies insidefloat + U525 grams
216 pennies insidefloat + V571 grams
235 pennies insidefloat + W616 grams
The Batons above are most accurate if you use relatively new pennies! Older pennies get worn and do not weigh as much, which could cause very minor changes in the accuracy. The Batons and Floats will still be fine and extremely accurate, just not quite Laboratory quality accuracy!

These floats can also be made out of 1" thick blue foam building insulation. The 'float' would be cut as a rectangle of 6" by 12.5". The 'FLOAT' would be cut as a rectangle of 10" by 15". Such floats are not very durable and are fairly easily damaged, where chunks can get lost and their accuracy then degrades. If you expect to use this system more than rarely, you should probably make one of the other types of float and FLOAT


An Optional 'Y' baton for larger people
3" standard PVC pipe 16.375" longY

An Optional 'Z' baton for larger people
4" standard PVC pipe 13.125" longZ

NOTES:
This entire set provides 264 possible different Baton choices that can be used for determining the Average Body Density and then the Bodyfat Percentage, 72 involving net flotation and 192 that involve net weight. This range should be sufficient for virtually any person.

In general, the Optional Y and Z batons may not be needed, as they are necessary only for larger people. You might look at the Analysis Charts (linked below) to see if you might need to use a Y or a Z baton.


Making these batons yourself is a fun project!


Some comment needs to be made about various popular "formulas" which are alleged to convert the average body density value (which is absolutely reliable and accurate) into a "Bodyfat Percentage". There are a couple such formulas that are very popular and assumed to be correct by many people:

Brozek formula is: (4.57/(body density) - 4.142) * 100

Siri (2-compartment) formula is: (4.95/(body density) - 4.50) *100

These formulas are a little misleading. First of all, they absolutely require expelling ALL the air possible from the lungs, something that takes some practice to do very well. But then they have to be adjusted for two different effects that they never mention! Even after you expel all the air you can from your lungs, there is still a Residual Volume of air remaining in the lungs. This amount varies from person to person but it is assumed to be 1.2 liters of volume. If a man displaced 91 liters of water, this would represent an adjustment of adding 1.319% (.01319) to the measured body density. It would seem that they could have just adjusted the Siri 2-compartment formula to become (4.886/(measured body density) - 4.50) * 100. If this man's body density happened to be the same as the water (0.9978 gm/cc), we would therefore have different calculated values of: (Brozek) 36.9% bodyfat or (Siri) 38.6% bodyfat. The adjusted readings are therefore around 6% lower than above, but still VERY high numbers!

I can use myself as an example. After exhaling NORMALLY, I still float. I weigh 202 pounds (and am 6'2") (my waist is around 33", relatively slim). With that NORMAL exhale, I can usually just sink using the X+D Batons but usually still float with the X+C Batons. You can see from the web-site calculator that my average MEASURED body density is therefore between 0.9891 and 0.9895 (gm/cc). (Note that this is a precision of one part in three thousand!) From our web-site calculator, that gives an estimate of between 26.2% and 26.5% bodyfat. From the American Council on Exercise guidelines, this is a little above the very top end of Acceptable. I had spent a career as a semi-pro volleyball player (when it was lower) and the result seems to me to be within a few percent of reality.

Note that our Calculator estimates the correction regarding how much air is still in the lungs and gets 1.0129 as an adjusted average body density. Below, we will see that with an absolute maximum exhale, we will get a very similar figure.

You can calculate that the above (unadjusted) Brozek formula as giving 49.1% and the Siri formula as giving 51.8% for me! Since "morbidly obese" is 35% or higher, those formulas might suggest that I probably don't fit through doorways! (Have you ever seen a winning beach volleyball player who was spectacularly obese?) It seemed obvious that those simple and crude formulas are sometimes very inaccurate! By the way, on the BMI Chart (height/weight) I am at 26, surprisingly close to what seems actually true! However, there is a reasonable explanation! When I really exhale ALL the air I can, I can avoid floating with the 'float' float and 'N' Baton. This means a measured body density of 1.0009. Our web-site bodyfat calculator gives a value of 26.6%, again in rough agreement with BMI and the other figure. With the adjustment for the Residual Volume of air in the lungs, the adjusted body density is 1.0139. This would give a Siri 2-compartment bodyfat value of 36.5%. This is closer but still apparently about 10% higher than we think it really is.

Careful scientific study has been done on such formulas, and it has been found that the Siri 2-compartment formula gives results that have a 95% confidence interval ranged from 8.1% to 12.0% bodyfat percentage, for different ages and genders studied, as compared to methods that are considered to give reliable results. So even though the Hydrostatic Weighing procedure provides excellent accuracy regarding the Average Body Density, these formulas for converting that to bodyfat percentages can have huge errors! And if the 95% confidence is sometimes off by 12.0%, that means that there are times when it is even worse than that!

When we discovered the large probable errors of such formulas, we developed a complex equation that is based on considering and analyzing each of the many different types of things that are inside our bodies (bone, blood, muscle, fat, organs, brain, skin, etc) and the quantities of each inside us. We feel that our very complex equations (about twenty factors, each of which has a density value and a volume value, or 40 total variables) are far more scientifically based than the popular formulas presented above. However, our bodyfat numbers tend to be less than the Brozek or Siri numbers seem to imply. We are still investigating this matter. Our web-site bodyfat calculator (linked below) uses our complex formula.

The main concept of our system is to know INCREMENTAL changes in average body density, which our approach certainly does to better than one part in a thousand. We didn't necessarily intend to generate truly precise NUMBERS claiming a specific bodyfat percentage. Once an average body density is determined, the different formulas (and our equations) give different numbers for bodyfat percentage, true. But again, what WE see as important is whether that number goes up or down, and not necessarily the size of that number! See the point? So you really could use the Brozek or Siri formulas with our system, and still see changes, good or bad, just that the numbers will be a lot higher.

As to being able to brag about some specific number as being YOUR bodyfat percentage, our research suggests that nearly any number you might claim has a high likelihood of being substantially incorrect. But we suppose that if it is a number that you LIKE, you will probably want to tell people what it is!

We expect to some day modify our equations, as better figures for organ densities and bone densities, etc, become available. This might especially be true for kids, who tend to have a higher proportion of dense bones! Well, we concede that SOME people will insist on using one or the other of those two popular formulas above, so we are providing (below) analysis charts which use those formulas. You are free to use any of the three, as they will all show improvements or back-sliding equally well! Just stay with whichever one you start with!


The Analysis Charts for the Filled PVC Batons or the Pepsi bottle Batons are:
For body weights of up to 130 pounds
For body weights of between 130 and 230 pounds
For body weights of between 230 and 330 pounds
For body weights of between 330 and 430 pounds

They are also available as Word (DOC) files which can be printed out and laminated to be around a swimming pool!:
For body weights of up to 130 pounds
For body weights of between 130 and 230 pounds
For body weights of between 230 and 330 pounds
For body weights of between 330 and 430 pounds


The Analysis Charts based on the Brozek formula are:
For body weights of up to 130 pounds
For body weights of between 130 and 230 pounds
For body weights of between 230 and 330 pounds
For body weights of between 330 and 430 pounds

The Analysis Charts based on the Siri formula are:
For body weights of up to 130 pounds
For body weights of between 130 and 230 pounds
For body weights of between 230 and 330 pounds
For body weights of between 330 and 430 pounds

The (blank) Progress Chart is at:
Weekly or Monthly Progress Chart

Notes on the Analysis Charts

This system works excellently and repeatably for ANY person. As mentioned in the main page discussion, for the very best repeatability for a Progress Chart, it makes sense to consider the meal and liquids and bodily functions in the hours before doing weekly testing. Otherwise, intestinal gas can increase the necessary Baton weight needed for neutral buoyancy.

There is another issue to mention. The Analysis Charts were created using certain assumptions regarding the proportion of different kinds of component materials in the human body, and also assumptions regarding the densities of those component materials. It turns out that some people, such as African-Americans, generally have bones that are of higher density than in others. There are also different proportions of body components in different people, such as big-boned or petite body types. These things can cause a shift in the numbers found in the Analysis Charts. For example, many African-American males might normally sink in a pool, due to their high-density bones. Some kids tend to naturally sink too! That does NOT necessarily mean that they are "professional athletes" as the very low Chart percentages might seem to suggest! They just have different internal body structures from most people. Therefore, the Analysis Charts could possibly provide numbers that are actually lower than their actual bodyfat percentage.

However, for the purposes of this testing, that effect is essentially unimportant! The person will always have the SAME high-density bones! Therefore, if the following week, a slightly lighter baton is needed (still with the float baton) progress is still shown in a Progress Chart. The actual numbers might be lower than what is real, but any improvements or other changes will still be clearly seen.


Finally, for "purists" and those with rigid scientific attitudes, we provide a set of the equivalent Measured Average Body Density for each cell in the Analysis tables.

For body weights of up to 130 pounds
For body weights of between 130 and 230 pounds
For body weights of between 230 and 330 pounds
For body weights of between 330 and 430 pounds

These values are true and accurate, without any mathematical assumptions regarding proportions of fat, bone, blood, etc, and without any assumptions regarding the precise density of those components. Technically, these values are all that are really needed for this system! However, the general public is less interested in claiming an average body density of 1.0074 gm/cc than in simply claiming a bodyfat percentage! Technically, these charts show WHY this system works and why it is so precise, although we realize that most people will never want to use them!

These density charts, and the other Analysis Charts, were calculated assuming that the the pool water was at around 72°F and therefore had a density of 0.9978 gm/cc. If the pool water was cooled to 39°F, its density would be the 1.00000 gm/cc that books indicate. We note that public pools are nearly always within a few degrees of the same temperature, but even backyard pools rarely change by even 10°F. It turns out that when you DO do the calculations, the difference between doing this in a 70°F pool and an 80°F pool, is less than one part in a thousand. Yes, that might cause the "one part in a thousand density difference" that we described above, but that tiny amount is usually only equal to about one Baton letter difference. And that's for a very cool pool compared to a bathwater pool! NOT a factor!


You can actually get a ball-park number for your bodyfat percentage without making these things, which is likely to be within about 10% of your actual bodyfat number. You need a swimming pool and a friend!

Have a "normal" amount of air in your lungs, NOT having severely exhaled or inhaled. And then simply float stationary! Your friend sees (or maybe even measures) how much of your head sticks out of the water! If you do NOT float and sink toward the bottom, your bodyfat is likely to be around 13% or lower. If your friend sees TWO INCHES of the top of your head above the water, you are likely to be around 24%. If your friend sees about FOUR INCHES (essentially to the very top of the earlobes), you are likely to be around 40%. If around SIX INCHES (essentially to the earholes, and your eyes are above the water) then you are likely to be around 57%. You might see from the large changes in bodyfat numbers due to rather small differences in the amount of the head being visible, that this method is only very approximate, with plus-minus 10% being expected. It only provides a ball-park number!

We mention this because there are a LOT of people who have been told that they have 8% or 4% or 11% bodyfat, due to using the extremely inaccurate bodyfat caliper method or electrical impedance (methods absolutely proven to regularly be 15% off either way, so in other words, meaningless except for bragging purposes.) A person could try to alter this method by intentionally normally exhaling first, which makes you float around one inch lower, which would appear to give an estimate of around 6% lower. By attempting to exhale all the air you can, you can lower your body by about 3 inches, which can give the appearance of around 16% lower estimate. The point is that by simply altering the amount of air in your lungs, you could change this reading by as much as 16%, another indication of why the far more accurate and repeatable Batons and Floats are desirable. If you really want to believe that you are at 8% or 11% so you can brag to your friends, there are many ways you can create such a number. However, if you actually want a REAL number for bodyfat, this very crude method can get you within about plus-minus 10%, and the Batons-Floats can get you within about 1%.


The main presentation page is at: Bodyfat - Accurate and Easy Determination
Bodyfat - Combating Childhood Obesity Through Motivation (specifically directed at Childhood Obesity)

The page that has the Bodyfat Percentage - Determining Accurate Bodyfat Easily Bodyfat Calculator which uses the Baton/Float letters and the dry body weight can calculate the correct density and bodyfat values for essentially anyone between 30 pounds and 800 pounds and with essentially any percentage of bodyfat.

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