The Difference Between Muscle Weight vs. Fat Weight

If you live in a human body, you probably already spend some serious time thinking about fat vs. muscle — maybe because you want to make some changes to your body. Or maybe just because we all live in a culture flooded with messages about body types, diets and exercise.

So, understanding some facts about muscle and fat — things like how much a pound of muscle weighs compared to a pound of fat (Spoiler alert: They weigh the same!) and their actual function — can be helpful as you consider your own body and health.

To learn a bit more about fat vs. muscle, we talked with psychologist, exercise physiologist and registered dietitian David Creel, PhD.

“Muscle vs. fat is sometimes the one topic people want to talk about — or don’t want to — depending on their situation,” notes Dr. Creel. “And it is important, though not the only consideration, in determining overall health.”

How do you compare fat and muscle?

While we might think we already know the difference (I can’t define fat, but I know it when I see it!), there are important differences between fat tissue and muscle tissue that can help us understand them better.

The main role of body fat is to serve as an energy reserve in your body. It plays a key role in a surprising number of other areas, too — from regulating glucose and cholesterol to contributing to immunity.

Of course, fat can also be the “bad guy” when we let it have the run of the place. Excess fat can lead to having obesity and increase your risk of diseases like diabetes, cardiovascular disease and even certain cancers. Some research concludes even if you have a healthy BMI (body mass index), a high body fat percentage is linked with increased mortality. In other words, carrying a lot of body fat can increase your risk of dying earlier.

But muscle tissue is what doctors and scientists refer to as “metabolically active” — meaning that it takes energy to maintain itself. In other words, muscles burn calories. And it even does that when we’re at rest. Building up and keeping muscle mass is important for your overall general health and for enhancing your physical abilities.

Building up muscle has an obvious benefit — if you’re building muscle, you’re not losing muscle, which naturally occurs with aging. And muscle gain also helps improve bone density. Both can help people to stay active as they get older.

Not only that, but Dr. Creel says that having more muscle — and so, less fat — may improve your sense of well-being. Simply put, if you’re in better physical health, you’re likely to feel better about yourself.

Am I gaining weight in muscle or fat?

Knowing the answer to this often-asked question requires knowing a bit more about your body composition.

And we’re not just talking about a popular measurement like BMI, or body mass index, here. BMI only estimates what a person should weigh based on a certain calculation (multiply your weight in pounds by height in inches squared — and then multiply by a conversion factor of 703).

But that doesn’t reveal your true body’s mix of muscle and fat. You’ll need some help to know that, either from a medical provider or by using a commercial product (you can even shop online for handheld fat measurement devices).

A medical provider may use other methods to determine the makeup of your body — from MRI (magnetic resonance imaging) to a DEXA scan (bone density test) to bioelectrical impedance (using a small electrical current to measure the difference in electrical conductivity between the body’s muscle and fat tissue).

Other tools include measuring waist circumference and measuring skin thickness using skinfold calipers in certain areas of your body, such as the back of your upper arms and under your shoulder blades.

Generally, you’re aiming for a body fat percentage in the range of 14% to 24% for men and people assigned male at birth and 21% to 31% for women and people assigned female at birth, according to the American Council on Exercise (ACE). Women tend to have higher body fat percentages due to reproductive needs and differing physiological makeups, according to the ACE.

Those percentages would be lower yet for athletes, but you would fall into the “obese” category if your body fat percentage is above the higher number.

In any case, once you know more about what your muscle-to-fat ratio is, you’ll have a baseline for tracking it to see results from exercise or a healthy diet.

Why am I gaining weight but looking thinner?

Let’s quickly get past an odd question that sometimes pops up. Maybe you’ve heard this one: “Which weighs more, a pound of muscle or a pound of fat?”

Short answer: They weigh the same (a pound is a pound!). But they sure don’t look the same.

In other words, a pound of fat has a much larger volume. But a pound of muscle appears leaner and more toned. So, an extra 15 pounds of fat will take up a lot more space in your body — giving you a softer appearance. And muscle is denser, meaning it has a smaller volume for its weight. So 15 more pounds of muscle would make you appear firmer.

So, yes, you may be gaining weight, but also getting fitter.

“People who are only going by the numbers on the scale might become fixated on only losing weight and that might mean losing valuable muscle,” Dr. Creel notes.

Finally, if you’re especially interested in muscle vs. fat or body composition because you’re looking to get into “body recomposition” (a term borrowed from bodybuilders and weightlifters and now a hot topic in fitness circles), it’s even more important to understand the facts about fat weight vs. muscle weight, and why it all matters.

Can I weigh more because of muscle?

Yes, definitely.

But your total body weight isn’t necessarily an accurate marker of how healthy you are or what health conditions you’re at risk for — or how you feel.

Dr. Creel doesn’t have to look far for an obvious example.

“If you just go by BMI — my weight for my height, basically — I’m in the overweight range,” he says. “But a lot of my body composition is actually muscle because I have a workout regimen that builds muscle, which does weigh more than an equal volume of fat.”

On the other hand, it’s important to not use that fact as a cover for the truth. You may weigh more because you’ve accumulated some fat tissue along the way as well. So, again, knowing your body composition could be the key to understanding what your next steps might be.

Aim to strike a balance with a regular exercise regimen and eating healthy. With these habits, you could reduce your fat and increase your muscle, resulting in improved health and a greater sense of well-being, Dr. Creel says.

“Knowing what muscle and fat do, how they function, is a good start,” he adds. “Knowing how to encourage one and discourage an accumulation of the other is the basics of good health.”