Your body mass is made up of two components: body fat and lean body mass.

People often use the terms “lean body mass” and “muscle mass” interchangeably, but they’re not the same. Lean body mass includes muscle mass, as well as bones and bodily fluid.

Muscle mass is the size of your muscles. It includes:

However, when people talk about muscle mass, they’re typically referring to skeletal muscle.

This type of muscle is important for mobility, balance, and strength. It’s a sign of physical function, which is why we’re always told to build muscle.

If you have low muscle mass, it means you have lower-than-average muscle for your age and gender. If you have high muscle mass, your muscle mass is higher than average.

Depending on your body composition, you can have low or high muscle mass with low or high body fat.

Muscle mass is difficult to measure. It also depends on many factors, including height, ethnicity, and fitness level.

There isn’t a lot of credible data on average muscle mass percentages. The only source with reliable information is a 2000 study in the Journal of Applied Physiology. In the study, researchers measured the muscle mass percentages of 468 men and women.

The following charts are based on this study. While new research is necessary, this data will give you an idea of muscle mass percentages for different age groups.

Muscle mass percentage averages for men

AgeMuscle mass percentage
18–3540–44
36–5536–40
56–7532–35
76–85< 31

Muscle mass percentage averages for women

AgeMuscle mass percentage
18–3531–33
36–5529–31
56–7527–30
76–85< 26

It’s not possible to determine your exact muscle mass percentage without expensive technology.

There are calculators, formulas, and scales that claim to measure muscle mass, but these options haven’t been proven to be accurate.

Here’s what you can do to learn about your muscle mass and lean body mass:

Use body fat percentage

One way to determine your lean mass percentage is to use your body fat percentage.

To get your body fat percentage, weigh yourself on a body fat scale.

A body fat scale uses bioelectrical impedance to estimate your amount of body fat. It sends an electrical current through your body. Since fat conducts less electricity than muscle, the current can measure how much body fat you have.

You’ll also need to enter your height, weight, gender, and age. The scale uses this data, along with the electrical current, to estimate your body fat percentage.

You can subtract this number from 100 to get your lean body mass percentage. For example, a person with 30 percent body fat has 70 percent lean body mass.

But remember, muscle mass is just one part of your lean body mass. Plus, body fat scales aren’t always accurate. The percentages are estimates.

Use a U.S. military formula

The U.S. military has a formula for estimating body fat percentage.

This method involves measuring the circumference of different body parts. These measurements are then used to determine your circumference value (CV).

Your CV and height are placed on a chart with precalculated body fat percentage estimates. You can use this number to estimate your lean body mass percentage.

If you’re a man, measure your abdominal and neck circumferences. Your CV is abdominal circumference minus neck circumference.

If you’re a woman, measure your waist, hip, and neck circumferences. Your CV is waist circumference plus hip circumference minus neck circumference.

While the military uses this method to assess body composition, it’s not the most accurate method. The circumference measurements don’t take into account muscle size.

Get an MRI

The most accurate way to calculate muscle mass percentage is to use magnetic resonance imaging (MRI).

An MRI uses strong magnets to take an image of your muscles. When you’re placed in an MRI machine, the magnetic field briefly rearranges your body’s hydrogen atoms. This releases energy, which the machine uses to determine your muscle mass.

MRI is the gold standard for determining muscle mass percentage, but it’s very expensive. It’s not a practical choice for estimating muscle mass percentage.

If you have high muscle mass, you have more muscle than is typical for your age and gender.

Benefits

Generally, greater muscle mass has positive health effects.

As you get older, you naturally lose muscle mass. This age-related muscle loss, also called sarcopenia, begins at age 30. You continue to lose 3 to 5 percent of muscle mass every decade, which reduces physical function and increases your risk of injury.

But if you have high muscle mass, you can slow down muscle loss and protect your physical ability.

Skeletal muscle also improves your overall metabolism. Compared to fat, skeletal muscle burns more calories at rest.

Additionally, greater muscle mass is associated with longevity. A 2014 study in the American Journal of Medicine found that older adults with more muscle mass live longer than those with less.

Side effects

If you have higher-than-average muscle mass, it may be difficult to find clothes that fit well. You’ll also need to eat more calories to feel full, which can become inconvenient and expensive.

Some people say having greater muscle mass reduces their flexibility and ability to jump or run.

Having low muscle mass means you have less muscle than is typical for your age and gender.

Benefits

There aren’t any real benefits of low muscle mass.

Some people say having more fat than muscle offers a survival advantage because excess fat can provide energy when the body is stressed. However, this benefit is hypothetical.

Side effects

Low muscle mass speeds up age-related muscle loss and reduces physical ability. This increases the risk of injury and disability.

Having low skeletal muscle mass is also associated with:

Although muscle mass declines with age, it’s never too late to build muscle through exercise and diet.

Exercise and good nutrition will also help preserve muscle mass as you get older.

Exercise

Strength training, or weight training, is the best way to build muscle mass. This type of exercise strengthens your muscles by forcing them to work against resistance.

You can:

It’s recommended to do two or three strength training sessions each week.

Cardio is still important, though. Aerobic exercise, like jogging or dancing, supports muscle growth and slows age-related muscle loss.

Diet

Gaining and keeping muscle mass also depends on good nutrition. This includes eating enough nutrient-dense calories to fuel your body.

Protein, which helps build and repair muscle, is particularly important. The amount of protein you need depends on your level of physical activity. Generally, 10 to 35 percent of your daily calories should come from protein.

Examples of high-protein foods include:

  • beef
  • poultry
  • fish
  • eggs
  • beans
  • nuts

You also need enough carbohydrates to fuel your muscles. If you’re strength training two or more times per week, carbohydrates should make up at least 50 percent of your daily calories.

Additionally, adequate intake of fat, vitamins, and minerals is necessary for building muscle.

It’s also best to limit or avoid processed foods as much as possible. By eating whole foods, like vegetables and eggs, you can help your muscles stay healthy and strong.

Muscle mass is a part of your lean body mass. Typically, the more muscle you have, the less prone you are to injury, chronic disease, and early death. Muscle mass also indicates physical function, including mobility and balance.

It’s difficult to calculate lean body mass, let alone muscle mass. The most accurate methods are expensive, and there isn’t a lot of reliable data proving their accuracy.

To better understand your physical fitness, it’s recommended to use your body fat percentage instead.