How to Calculate Your Fat & Muscle Mass

The amount of bodyweight someone carries does not distinguish between muscle and fat weight. Overall bodyweight does not paint a true picture of how well someone is doing regarding their diet and exercise. For example, when I step onto the scale, it tell me I weight 227 pounds, great. I’m more interested, though, in the ratio of that bodyweight number. Meaning, how muscle and fat do I currently have? What is the ratio of my lean muscle and body fat? This, in my opinion, is the more important question that we should ask ourselves every few months. As an example, my goal is 85 percent lean muscle and 15 percent body fat. If you are female gym-goer maybe that ratio looks like 75/25.

Muscle, water, connective tissue, organ weight and more are included as part of lean body mass.

Jefit Body Composition Metrics

The Jefit website offers the ability to record and track the five key health metrics seen below. There is also the ability to input and track bodyweight, girth measurements and percent body fat via Jefit iOS and Android platforms. What is great about the website, however, is the option to see your breakdown of lean muscle mass and fat mass. Check it out!

  • Current Weight
  • Percent Body Fat
  • Lean Body Mass
  • Body Fat Mass
  • BMI (Body Mass Index)

How to Calculate Fat & Muscle Mass

First, you need your bodyweight and percent body fat numbers. Once you have these, you can then figure out the ratio of muscle and fat mass that comprises bodyweight. A few items to keep in mind. Men have about 3 percent essential fat while women have about 13 percent essential fat. This is the minimal amount of body fat that someone needs to maintain for overall health.

The average college-age male, who is a non-athlete, has about 15 percent body fat, while a female of the same age will have about 23-25 percent. A college athlete will have considerably less body fat. Here are two examples that demonstrate how fat and muscle mass are calculated.

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Let’s look at the case study from above from a Jefit user. This is from a 227 pound male who is carrying about 17 percent body fat.

First, multiply bodyweight by percent body fat. The number you get is fat weight mass. In this case, it’s 227 x 16.8 percent = 38.13 pounds, which is the fat mass.

Next, subtract fat weight (38.13) from bodyweight (227), this equates to lean mass (not pure muscle mass) which in this case is about 189 pounds. About 44 percent of this number is pure muscle mass, which in this case, is about 83 pounds. The weight of your bones (skeletal system) comprises 15 percent of your bodyweight.

What the Math Looks Like

227 x 17 percent = 38 pounds of fat weight, therefore, 227 – 38 = 189 pounds of lean mass. It’s important to understand that this number, 189 is comprised of: muscle, bone, connective tissue, fluid, skin, organ weight, etc. Otherwise known as all the good stuff. The 38 pounds is fat or adipose tissue. The ratio for this male individual would be 83/17. Or, 83 percent lean mass and 17 percent fat mass.

Men carry more muscle than women. An average male (18-39 years old) has about 44 percent of their bodyweight made up of muscle mass. About 34 percent of a female’s bodyweight is made up of muscle mass.

Use Jefit to Record & Track your Body Composition Metrics

To ensure an exercise and nutrition program is truly working, record a few baseline numbers mentioned above. Over a period of time, you should experience a slight increase in lean mass, a decrease in fat mass and your ratio should also change. Recording and tracking body composition (and strength) metrics should help keep you motivated. An assessment can be beneficial because it keeps you consistent, with both training and your nutritional intake, because you know at a future date, your metrics will be looked at again for comparison.

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