How to Calculate Body Fat Percentage Using The Wisdom Of Crowds

What body fat percentage are you?

If you know the answer to this question, you’re in the minority.

Measuring your body fat percentage can be extremely expensive and surprisingly inaccurate.

This is bad news.

Knowing your body fat percentage is crucial if you’re an aspiring dieter because it allows you to calculate a realistic weight loss goal and plan your rate of progress accordingly.

Eric Helms, a 3DMJ bodybuilding coach, has helped hundreds of people diet down into contest level body fat percentages. In a recent Q & A video, when asked about the most common dieting pitfall he’s come across he said:

The number one most common mistake we see in our athletes is that they misjudge the time it takes to lose weight by 2-3 months. The average contest prep lasts 5-7 months, not 12 weeks.

That guy who thinks he’s 16% body fat but is actually 26% will never get those washboard abs from his eight-week magazine diet, no matter how motivated he is. And when the eight weeks are over, and he realises he still has another 30 pounds to lose, how resigned do you think he’s going to feel?

And we wonder why 90% of dieters fail

Don’t make this mistake.

Studies show that patients recover quicker when their surgeon tells them everything the operation will entail — even the gory details. I believe dieters can benefit from the same treatment.

It’s time to get real.

After you’ve calculated your body fat percentage, I’ll show you a formula for predicting exactly how much weight you need to lose to reach your body fat percentage goal. With this information, you can plan your weight loss journey accordingly.

5 Conventional Body Fat Percentage Measuring Systems

Lyle McDonald does an excellent job of explaining the different systems of measuring body composition in this article. I’ll provide a  brief introduction of each method before summarising the main pros and cons.

1. Body Mass Index (BMI)

BMI is simply the measure of relative weight based on an individual’s weight and height. If you have a high BMI, you’re too heavy relative to your height. A low BMI likewise means that you’re too light. 

Pros: It can be used to get a rough estimate of body fat percentage.

Cons: If you lift weights, which all people wanting to lose weight should be, it simply doesn’t work. Because it only measures weight and height, a lean 200lb bodybuilder will have the same BMI as a fat 200lb couch potato if they’re the same height.

2. Hydrostatic Weighing (Underwater)

Different tissues in the body have different densities and, therefore, have individual buoyancies in water. By weighing someone underwater and applying further calculations, a body fat percentage can be measured.

Pros: When done right, it can be very accurate.

Cons: It’s expensive, uncomfortable, and lengthy. Furthermore because total submersion is necessary, residual air in the lungs can skew the results. It’s far from foolproof.

3. Skinfold Calipers

The guy in the photograph at the top of the post is using a calliper. They’re probably the most recognisable method of calculating body fat percentage because they’re the cheapest and most accessible.

After measuring the skinfold thickness at various parts of the body, the results are totalled, put into an equation along with age and a body fat percentage comes out the other end.

Pros: Cheap, accessible, and when used correctly, quite accurate.

Cons: Large margin of error and variance among quality of calliper.

4. Bioelectrical Impedance Analysis (BIA)

BIA determines the electrical impedance, or opposition to the flow of an electric current, through body tissues which can then be used to calculate an estimate of total body water (electricity doesn’t flow through fat as other tissues). Total body water is then used to estimate fat-free body mass and, by difference with body weight, body fat.

Pros: You can buy relatively cheap BIA weighing scales and handheld devices that are easy to use and fairly accurate when used correctly.

Cons: Results vary depending on the hydration of the subject. A little dehydrated? Skewed results.

5. Dual-Energy X-ray Absorptiometry (DEXA)

DEXA scans are mainly used to measure bone density in patients, but they can also detect the density of muscle and fat tissues and calculate the percentage of each from your total body weight. This video of 3DMJ coach Alberto Nunez getting a DEXA scan shows the process and results you can expect from having one.

Pros: Very accurate, can highlight muscle imbalances.

Cons: While not extremely expensive, it still costs money and takes time and planning to book an appointment.

The following chart  was featured it the Tim Ferriss book The Four Hour Body (cliff notes). It gives a simple run down of the various methods of measuring body fat percentage:

body fat percentage chart

Using the expensive methods, like the DEXA scan, while accurate are an expensive hassle. Unless you’re loaded you probably won’t have one done more than once every few years.

The cheaper methods are great for tracking body fat percentage. If your skin folds are getting smaller each week, you’re probably losing body fat, but it’s not ideal for getting a highly accurate objective body fat percentage.

I propose a new method of calculating your body fat percentage. It’s free, accurate, and you can do it all from the comfort of your home.

But before I explain exactly what this method is, I want you to make a guess how heavy this ox is:

Wisdom of Crowds Ox

How heavy is this guy?

Yeah, I know it’s random but what do you think? 500lb? 1000lb? 2000lb?

Whatever your answer, unless you’re extremely lucky, you won’t get it right.

Why did I ask you how heavy this Ox weighs?

Well, if I told you that the person who guesses closest to the right number will get $1,000,000 transferred to their bank account, would you do anything differently to make a better-informed guess? Would you just pick a number that feels… ‘right,’?

There is a method of getting the answer correct within 1 lb., and it doesn’t involve any crazy technology. It’s the same method we’ll use to calculate our body fat percentages.

Wisdom of Crowds

Psychological illusionist Derren Brown claimed to use the ‘Wisdom of Crowds’ concept to explain how he correctly predicted the UK National Lottery results in September 2009. While his application of the concept remains dubious, his understanding of the psychology behind it, is not.

On his blog, he explains exactly what the wisdom of the crowds is all about:

Crowd behaviour is often associated with irrationality. Crowds form mobs and cults. They panic and the herd instinct is often wrong and easily swayed. At least that is the common perception. But scientist and polymath Francis Galton discovered that not all crowd behaviour was negative. Indeed he found that if you asked enough people the same question, they might come up with better answers than even the experts.

It was in 1906 that Galton made his discovery of what is known as the wisdom of crowds. He attended a farmers’ fair in Plymouth where he was intrigued by a weight guessing contest. The goal was to guess the weight of an ox when it was butchered and dressed. Around 800 people entered the contest and wrote their guesses on tickets. The person who guessed closest to the butchered weight of the ox won a prize.

After the contest Galton took the tickets and ran a statistical analysis on them. He discovered that the average guess of all the entrants was remarkably close to the actual weight of the butchered ox. In fact it was under by only 1lb for an ox that weighed 1,198 lbs. This collective guess was not only better than the actual winner of the contest but also better than the guesses made by cattle experts at the fair. It seemed that democracy of thought could produce amazing results.

However, to benefit from the wisdom of crowds several conditions must be in place. First each individual member of the crowd must have their own independent source of information. Second they must make individual decisions and not be swayed by the decisions of those around them. And third, there must be a mechanism in place that can collate these diverse opinions.

Internet search engines are a good example of the wisdom of crowds in action. It is the reason the pages you search for come up near the top of the search engine list. In general terms the more people are linking to a page and the more popular it is the higher it comes. Another highly visible example of crowd decision making can be found in the television game show Who Wants To Be A Millionaire. When the player does not know which one of four answers is correct, they can ask the audience. Each member of the audience makes a separate and individual vote for the answer they favour. These votes are then collected and the results displayed. Often it is obvious from the result that one particular answer has found favour. And that is the one the player generally goes along with. In 95% of cases it is correct.

Can you see how we can use this to estimate our body fat percentage? It’s so obvious it’s a wonder no one else has connected these two topics before.

Here’s how you do it:

Step one: Round up as many individual approximations of your body fat percentage as possible.

Step two: Add them up and average the results.

You can use the ‘conventional’ methods of estimating body fat percentage too if you want, but you don’t have to. I don’t.

Below I’ve listed the places where I get my body fat percentage approximations. They’re all free, and while not highly accurate individually, taken as a crowd, they work great.

4 Simple Methods of Calculating Body Fat Percentage

Now, while each approximation need not be highly accurate, it has to come from a somewhat valid source. Body fat percentage is quite an esoteric field, asking 10,000 school kids to make a guess won’t help. Just keep that it mind. We’re after quantity, but a little quality will only help.

1. Photographs

I highly doubt these folks had a DEXA scan and then reported their results online. More likely, someone guesstimated the body fat percentage of these people and posted their conclusions online.

Nevertheless, the images below provide a ballpark idea of where you might fall on the continuum. Make a guess, write it down. That’s the only approximation you’ll make of your own body fat percentage (people always underestimate how much fat they carry.)

body fat percentage for men and women

2. Local Gym

I assume you attend a gym. If you don’t, you should. Find some people who you trust up your local gym and ask them what body fat percentage they think you are. Take photographs, or take your top off if you’re feeling confident.

They can get a real good look at you, see how much fat you can pinch from your midriff and give you a solid estimation. Get a few of these if possible, write them down and add them to the pile.

3. Ask The Audience

As Derren Brown said in his ‘wisdom of crowds article,’ on the game show Who Wants To Be A Millionaire, the ‘ask the audience’ option yields the correct answer 95% of the time. If you go onto the post your pictures forum, you can post pictures of yourself and get loads of approximations from knowledgeable bodybuilders.

You might be afraid of putting pictures up of yourself in case people laugh and mock you. Don’t make this a self-fulfilling prophecy. Most people love giving advice and feeling part of a community. Hide your face if you want, but I encourage to put yourself out there, making yourself vulnerable is a sign of strength. It also helps you to become more objective about your physique – ‘I have fat’, rather than ‘I am fat.’

If you have a smartphone, you can download Bodyspace, a free app run by that allows you to post pictures and get feedback on your progress.

4. Online Body Fat Calculators

These calculators are used by the military to get a quick ballpark estimate of a person’s body fat percentage. They’re fairly accurate for what they are. Listed below are two slightly different formulas that you can add to your body fat percentage mixing bowl.

U.S. Navy Formula

U.S. Army Formula

When you’ve got all of your approximations (minimum of 5, the more, the better), add them all together and average the results. Here’s an example:

BF estimations: 14.3%, 15%, 11%, 18.8%, 15.6%

Finding the mean: 14.3 + 15 + 11 + 18.8 + 15.6 = 74.7 /5 = 14.94% 

So you know your body fat percentage. What next?

At the beginning of this article, I explained that people frequently mess up their fat loss attempts because they underestimate how much fat they have to lose, and then get burnt out and give up.

Now that you’ve learnt how to calculate body fat percentage using wisdom of the crowds, you can use this figure to estimate how much fat you’ll have to lose to reach your ideal body fat percentage. I picked up the following formula from Lyle McDonald’s Body Composition Calculations article.

It’s a simple two part equation:

Step 1 – Calculating Fat-Free Body Mass (LBM): 

Multiply total body weight by the body fat percentage expressed as a decimal.

Weight * body fat as decimal (10% would be 0.10, 34.7% would be 0.347)

If I weigh 180 pounds and my body fat percentage was 14.94% I’d input:

180 pounds * 0.1494 = 26.82 pounds of total body fat

Now that you know how much fat you have on your body, simply subtract your total body fat from your total body weight to determine fat-free body mass.

180 pounds – 26.82 = 153.18 pounds

Step 2 – Calculating Goal Weight

This is a slightly more complicated equation but still straightforward.

Current Lean Body Mass / (1-Goal Body Fat percentage as a decimal)

So if I wanted to be 10% body fat, my equation that would be:

153.18 / (1 – 0.10) = 170.2 pounds

So if my goal weight is 170.2 pounds and I weigh 180 pounds, I only have 9.8 pounds to lose. I can pace myself and allow plenty of time to lose that weight.

I strongly recommend you take the time to work out all of this stuff, losing weight without a solid plan is like sailing without a compass.

Meet the Creator

Jon Brooks

Jon Brooks is the author of ComfortPit and the co-creator of HighExistence and 30 Challenges to Enlightenment, the ultimate self-improvement obstacle course. He researches the practical ways art, science, psychology, technology, history, and philosophy can help us live more skillfully.

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