How to Calculate Body Fat Percentage

Most people who take weight loss (or gain) seriously want to know how to calculate body fat percentage.

That’s because tracking your body fat percentage over time (especially when trying to gain or lose weight) helps you measure the effectiveness of your diet and training plan.

Specifically, tracking your body fat percentage helps you to understand how successfully you’re . . . 

• Losing fat and not muscle during a weight loss phase (or cut)
• Gaining muscle and not just fat during a weight gain phase (or lean bulk)

In this article, you’ll learn everything you need to know about body fat percentage, including how to calculate your body fat percentage accurately at home.

What Is Body Fat Percentage?

For instance, if you use proper diet and strength training to increase your weight from 150 to 170 pounds and gain just 5 pounds of fat, your new body fat percentage would be about 12% (20 / 170).

If you then stopped strength training for a year and lost 10 pounds of muscle but no fat, your body fat percentage would still be about 12% (20 / 160).

So, your body fat percentage ebbs and flows as you change your body composition.

How to Calculate Body Fat Percentage

Body Composition Scales & Handheld Devices

For instance, if someone has a huge amount of subcutaneous fat, the current will avoid it and pass through internal tissue instead. This is perhaps why research shows that many two-electrode devices, like scales and handheld devices, are susceptible to missing entire portions of your body.

2. The body fat readings you get using BIA are predictions based on equations, and the methods used to create these equations often give inaccurate results. 

3. Research shows that testing conditions can greatly influence the readings you get when you use BIA. Studies show being dehydrated will cause your body fat percentage to register higher than it is, eating a large meal will cause you to register leaner than you are, and exercising shortly before the measurement makes it appear that you have more muscle and less fat than you really do.

In the final analysis, BIA readings are just too all over the place to be useful, even if you attempt to control factors such as hydration, food, and exercise. Don’t waste your time or money on them.

Body Fat Calipers & Skinfold Testing

1. If you grab too little skin and fat you’ll get a falsely low reading. Grab too much and you’ll inflate your readings.
2. Research shows the equations used to convert skin thickness readings into a body fat percentage can spit out wonky results.

It’s no wonder studies show skinfold testing can miss the mark by up to 6%. This is true even when the testing is done by people who are familiar with how calipers work, like bodybuilders and personal trainers.

That said, although skinfold testing isn’t a foolproof method for determining body composition, it has its uses (more on this in a moment).

Pictures and the Mirror

Dual-Energy X-Ray Absorptiometry (DXA)

• Results can vary between machines, even if they’re produced by the same manufacturer.
• Algorithms used to convert raw data into body composition measurements differ and thus outputs can differ.
• The type of X-ray used influences the results.
• Like BIA, hydration status can significantly impact DXA results (even minor changes in the hydration levels of lean mass can be enough to skew results).
• Results are affected by gender, body size, total fat mass, and even disease state.

For example, two studies found that individual error rates using DXA went as high as 4% (absolute!).

In another study, individual error rates in the range of 8-to-10% were seen. In yet another, DXA significantly overestimated decreases in body fat and underestimated increases.

The Bod Pod

The Bod Pod is a machine that measures the amount of air your body displaces inside a sealed chamber and uses equations to translate this into an analysis of body composition.

However, the Bod Pod’s results are affected by all kinds of things like . . .

 . . . which is why studies show that it can be off by between 5 and 15%.

Magnetic Resonance Imaging (MRI)

The accuracy of MRI is largely dependent on how many of these images are taken. Research shows that trying to estimate body fat based on a sparse set of “slices” gives an imprecise reading of body composition.

Unfortunately, unless you’re willing to part with large sums of money and spend a considerable amount of time in the thin tube of an MRI scanner, the body composition data you get from MRI is not particularly accurate. 

This is why MRI is generally only used to measure body composition in scientific studies, where many images can be taken.

How to Calculate Body Fat Percentage at Home Accurately

Weigh yourself daily and calculate an average every 7 to 10 days.

Your weight fluctuates every day due to things like water retention, glycogen storage, and bowel movements (or the lack thereof).

That’s why flogging yourself over small unwanted increases or decreases in weight is silly and counterproductive. Instead, work with weekly averages, which will show you what’s really happening with your weight.

Weigh yourself first thing every morning, naked, after the bathroom and before eating or drinking anything

Then, after seven days, add up your readings and divide the sum by seven. That’s your average weight for that week.

Watch those averages over time and you’ll be able to see if things are actually moving in the right direction or not. A good rule of thumb is to only adjust your diet and training regimen if your weight is stalled for two weeks or more.

Take weekly caliper measurements.

In terms of what caliper to use, I like the Accu-Measure skinfold caliper because it’s affordable, easy to use, and as accurate as more expensive models. 

Since it’s possible to lose or gain fat faster in some places than others, I recommend you take three skinfold measurements in various places on your body:

• If you’re a woman, take a triceps, thigh, and suprailiac measurement.
• If you’re a man, take a pectoral, abdominal, and thigh measurement. 

And if you have your heart set on using these measurements to compute your body fat percentage, and are prepared to take the results with a grain of salt, you can use the Legion Body Fat Percentage Calculator to estimate your body composition.

Take weekly waist measurements.

There’s nothing fancy that you need for this—a simple measuring tape will do. That said, you’ll probably find this model from MyoTape easier to use, especially if you don’t have a friend to help take your measurements.

Take weekly pictures.

If you want to learn more about the art and science of measuring your body fat percentage, check out my bestselling fitness books Bigger Leaner Stronger for men, and Thinner Leaner Stronger for women.

How to Calculate Body Fat Percentage from BMI

While it’s a quick and convenient way to estimate whether you are a healthy weight for your height, it doesn’t measure your body fat percentage directly, and thus can’t be used to predict body fat percentage accurately.

That said, researchers have tried for decades to come up with an equation that uses BMI to accurately calculate body fat percentage.

The most recent of these equations states that body fat percentage is . . .

(1.39 x BMI) + (0.16 x age) – (10.34 x gender) – 9 = Body Fat Percentage

(In this case, “gender” is equal to 1 for men and 0 for women. This accounts for men’s lower body fat percentage.)

To use this formula, you’d first calculate your BMI using the Legion BMI Calculator. For example, I’m 37 years old, 6’1 and weigh about 190 pounds, which means my BMI is about 25. 

Here’s what the math would look like for me . . .

(1.39 x 25) + (0.16 x 37) – (10.34 x 1) – 9 = Body Fat Percentage

34.75 + 5.92 – 10.34 – 9

40.67 – 19.34 = 21.33% body fat 

. . . which is exactly why you can’t use BMI to estimate body fat percentage. 

In reality, I’m currently sporting a six-pack at about ~9-to-10% body fat, or about half what this formula predicted. 

This doesn’t mean this formula is useless, but it has a major limitation: it was designed and is best suited for estimating the body fat percentage of people with average levels of body fat (anywhere from 15-to-25% or so), and considerably less accurate if you’re very lean, or overweight.

If you want to accurately calculate your body fat percentage, you’re better off steering clear of BMI equations and using caliper and waist measurements and pictures instead. 

FAQ #1: What’s the ideal body fat percentage?

FAQ #2: How lean do I need to be to get great abs?

Luckily getting to this body fat percentage is easy to do. A bit of proper dieting, weightlifting, some cardio, and a little patience is all it takes.

FAQ #3: What’s the lowest body fat percentage I can maintain?

Try to maintain a lower body fat percentage than this for longer than this, and you can run into a long list of negative consequences, including: 

What’s more, muscle and strength gain will also be impaired if not stopped altogether, which is why staying this lean can be counterproductive over the long haul.

FAQ #4: How do I lower my body fat percentage?

Reducing your body fat percentage is mostly a matter of controlling and optimizing your diet and doing a moderate amount of strength training. Since diet is the long pole in the tent when it comes to fat loss, here are a few tips for proper dieting: 

1. Determine how many calories you should eat every day.

Research shows that eating 20-to-25% fewer calories than you burn every day will help you lose fat lickety-split without losing muscle or wrestling with excessive hunger, lethargy, and the other hobgoblins of low-calorie dieting.

2. Determine how much protein, carbohydrate, and fat you should eat every day.

If you want to lower their body fat percentage without encountering problems with body composition, workout performance, and overall health and well-being . . .

• Set your protein intake to 40% of your total daily calories.
• Set your carbohydrate intake to 40% of your total daily calories.
• Set your fat intake to 20% of your total daily calories

3. Create a meal plan based on these numbers.

Or, if you’d like professional help putting a meal plan together (not to mention guaranteed results), click here to learn about my diet coaching service.

FAQ #5: What is the average body fat percentage?

In the United States, the average body fat percentage for men is 28%, and the average body fat percentage for women is 40%.

In other words, most Americans have about twice as much body fat as they should in order to look athletic and stay healthy.