One cup fat weight(left)– 7.5oz
One cup muscle weight(right) — 9.7 oz
Equal volume fat weighs approximately 80% of what muscle weighs.
I love it when my patients lead me to learning something new. Recently I had a guy who asked me what is the difference in weight of one cup of fat vs. one cup on muscle? We all know muscle weighs more than fat. I was puzzled about the actual difference in weight with an equal volumn of each.  So…… we got to do some research and this is what all of us in my office and the patient learned.
Muscle is more metabolically active than fat, meaning it burns more calories when you are at rest which is why you want to increase and maintain a high percent muscle on your body. Muscle takes up approximately four-fifths as much space as fat. Two people may be the same age, height, weight, but the person with a higher body fat percentage will wear a larger clothing  size. This is another reason you should focus on total fitness and not just the ‘scales’. You can be thin, yet too fat. We call this skinny fat because you have very little muscle composition.
Muscle does weigh more than fat because it is a denser product.  On average, the density of fat is 0.9g/ml. The density of muscle is 1.1 g/ml.  Using the averages, 1 liter of muscle weights 1.06 kg or 2.3 lbs., while 1 liter of fat weights .9 kg, or 1.98 lbs.  An easier way to think of it might be: if you have an equal volumn of fat and muscle, fat is going to weigh about 80%  of what the muscle weighs. This can vary due to numerous factors including race, being extremely lean or being extremely obese according to “Exercise Physiology” by William D. McArdle, et al.
The ‘take away’ points are:
Yes, muscle weighs more than fat. But….. do not assume because you started working out and you are not losing weight it is because you are increasing muscle. It is most likely there is still some extra food intake.
The higher percent muscle you have on your body the smaller your clothing size because muscle takes up less space than fat.
Make sure your work out routine includes resistance work not just cardio.   Regardless of your age you should be working to increase muscle mass and maintain the muscle  you have. The higher percent muscle on your body the more calories you burn even while sitting in a chair or sleeping and the smaller your body mass. cb