The average Lean Body Mass (LBM) varies by sex and age — 60-80% in men and 50-70% in women. More than 75% LBM in men & 68% in women may indicate health concerns. To build a fit and healthy physique, you’ve got to understand your body composition. Standing on a scale will tell you how much you weigh but won’t shed light on how much muscle and fat you carry. For that, you need to know your lean body mass. Whether you’re an athlete focused on performance enhancement, a lifter wanting to pack on some muscle, or a senior trying to negotiate the changes that come with aging, a comprehensive understanding of lean body mass is needed to make informed decisions about nutrition, exercise, and well-being. In this article, we’ll break down everything you need to know about lean body mass, including what it is, how to calculate it, the factors that influence LBM, and how you can increase your lean body mass percentage. We’ll also reveal the average lean body mass so you can see how you compare to the rest of the population.
Average Lean Body Mass For Men and Women
The American Council on Exercise regularly publishes body fat percentage statistics. By subtracting these percentages from 100, we can determine Americans’ average lean body mass. The following statistics are sourced from ACE. (1)
Average Lean Body Mass Percentage by Age for Men:
Age Category Average LBM
Average Lean Body Mass Percentage by Age for Women:
Age Category Average LBM
These figures do not paint a pretty picture. It shows that the average American is carrying too much body fat and far too little muscle mass. We clearly see this when we compare the above statistics to the lean body mass standards. The following chart shows healthy lean body percentage ranges by age:
Age Healthy LBM Women Healthy LBM Men
20-39 68-79% 81-92%
40-59 67-77% 79-89%
50-69 65-76% 76-87%
Understanding Lean Body Mass
Your lean body mass (LBM) is a measure of your fat-free weight. It includes the following:
Your LBM will include a small amount of essential fat contained within the bone marrow and your internal organs. Essentially, though, it is how much you weigh when your body fat percentage is taken out of the equation.
How to Calculate Your LBM
The most precise way to calculate your lean body mass is with a DEXA scan. This involves the use of low-dose X-rays to measure bone density, lean muscle mass, and fat mass. However, this method may not be readily accessible and is quite expensive. You will have to make an appointment at a clinic that offers the service, with the cost being between $100 and $300.
Fortunately, there is a much more accessible and cheaper way to work out your LBM. Here’s a four-step method that will give you a relatively accurate result. You will need a body fat scale for the first step. These scales are relatively inexpensive and usually quite accurate:
Step One: Check your weight and body fat percentage on a body fat scale. Let’s say you weigh 200 pounds, and your body fat percentage is 20 percent.
Step Two: Subtract your body fat percentage from 100. This gives you your lean body mass percentage. In the above case, your lean body mass percentage would be 80 percent.
Step Three: Divide your LBM percentage by 100. This gives a result of .80 in the above example.
Step Four: Multiply your Step Three result by your body weight. This will tell your lean body mass. So, a 200-pound person with 20 percent body fat will have an LBM of 160 pounds.
Here’s an example of a female carrying 30 percent body fat at a body weight of 150 pounds.
Step One: 150 pounds / 30 percent body fat
Step Two: 100-30 = 70 percent lean body mass
Step Three: 70 /100 = 0.7
Step Four: 150 / 0.5 = 105 pounds of lean body mass.
So, the 150-pound woman has an LBM of 104 pounds. That means that she is carrying 45 pounds of body fat. If she lost half of that body fat, her physique and general health would improve dramatically. So, a good goal for her would be to lose 22 pounds.
If you want to avoid the math, you can use our lean body mass calculator to work out your LBM.
Why You Must Know Your LBM
Our objective in altering body composition is to boost lean muscle while reducing body fat. Without knowing these metrics, you’re merely speculating about your progress. In my experience as a personal trainer, most people are obsessed with weight loss. Their one and only goal is to drop pounds on the scale. TV shows like The Biggest Loser perpetuate the idea that dropping weight is all that matters.
But the scale (unless it’s a body fat scale) won’t tell you whether you’re losing fat or losing muscle, bone tissue, or something else. Since muscle tissue is denser than body fat, you might lose significant fat and gain a bit of muscle without any change on the scale. Or, if you gain a little bit more muscle, you may actually see an increase on the scale.
From what I’ve seen, people often panic when they notice an increase on the scale after a month of consistent exercise. Only when they are educated about the difference between body fat percentage and lean body mass do they come to appreciate that their body composition is changing for the good.
The bottom line here is that unless you are monitoring your lean body mass, you are essentially operating in the dark. It is essential to have a clear understanding of your body composition in order to make informed decisions about your health and fitness goals.