#MondayMythBuster: Does muscle weigh more than fat?

January 11, 2018
Cecilia Harris
There is not one Personal Trainer who hasn’t heard this question over and over again. Dr Paul says that even working over 20 years in the health and fitness industry that he can’t help but smile a little as people discuss which weighs more, fat or muscle? With the release of our excellent gym plan Dr.Paul thought he'd set this record straight once and for all.


This question always reminds me of a joke my father used to say when I was a child.  "What weighs more ... a tonne of feathers or a tonne of stones?" Having a more simpler way of thinking back then, the saying "as light as a feather" springs to mind so I proudly and excitedly claimed the right answer to be (of course) “Stones”.

Then I would hear a cackle from my father and he would say “they are EXACTLY the same weight!"  I would screw my face up, get annoyed, throw my milk on the floor and get very confused!

Of course, as an adult the equation is very simple, you could replace feathers and stones with bricks, wood, plastic, dumbbells, glass.... whatever, and the answer will always be the same because the key word is the measurement "Tonne".

The question of course gives us the answer. We have the information that both stones and feathers, weigh a "tonne" so regardless of what the material is, if they both weigh a tonne then of course they will be the same weight.  If I rephrased the question "What is heavier, 5 tonnes of feathers or 2 tonnes of stones?" this may be still difficult for most children to process. But of course, the correct answer in this case would be the 5 tonnes of feathers, because 5 tonnes is a heavier measurement than 2 tonnes. If a child still struggles to comprehend, then phrase the question "What is heavier, 5 tonnes of Stones, or 2 tonnes of stones".  Assuming they have some grasp of numbers then they will go for the correct answer of 5 tonnes of stones, this may be easier to process because they are not being confused by the image of feathers which are perceived as light.

To get a little bit more specific, if you can imagine how large a tonne of stones would look like, depending of course on the type of stone being used a couple of large wheelbarrows full may be enough to give you a tonne of stones.  However, if you tried to create a tonne of feathers, 2 wheelbarrows worth wouldn't be anywhere near enough. In fact you'd probably be getting into the realm of a few large lorries worth of feathers dumped over a football pitch.  So, the key point here is that a tonne of stones takes up much less space than a tonne of feathers would.  They of course both weight the same because they weigh a tonne, but the volume required of how much space is taken up, would obviously be much larger for the feathers.


 So, you are probably bored with my traumatic childhood experiences right now. You’re probably thinking, “so how does this apply to the question, which is heavier, muscle or fat?”. We often hear the question, which is heavier 1 kilogram of muscle or 1 kilogram of fat?.  As you can see this is exactly the same format of the question to which is heavier, a tonne of feathers of a tonne of stones.  As we have specified that it is 1kg of muscle, and we have specified that it is 1kg of fat, then of course the answer is the same. 1kg is 1kg, regardless of whether this is made up of fat, muscle, cotton, bricks, diamond or whatever.

And again, with the stones vs feathers scenario, if we had 1kg of pure fat and 1kg of pure muscle we know that muscle would take up much less space.

So, as you can see from the picture above, the weight of the fat and the muscle are exactly the same however the fat is taking up much more volume, much more space than the muscle.

This is because muscle is denser than fat, which in simplistic terms means it takes up less space than fat.  If you want to go a bit more complex; since muscle is denser, muscle does weigh more than fat if you compare same-size portions. On average, the density of fat is 0.9 g/mL. The density of muscle is 1.1 g/mL.  Using the averages, 1 litre of muscle weighs 1.06 kg, or 2.3 lbs., while 1 litre of fat weighs .9 kg, or 1.98 lbs. This may vary due to numerous factors including race, being extremely lean, or being extremely obese, according to “Exercise Physiology” by William D. McArdle, et al …but in a nutshell muscle will take up less space than fat!!

 So if you think of this in terms of a human body, Two people may be the same height and weight, but the person with a higher body fat percentage will wear a larger clothing size.  This is due to the fact that even though both people weight the same, the "larger" person has a higher percentage of their weight coming from fat.  This as we have learnt takes up more space.  So, they weigh the same, they are the same height, but due one of the individuals having more fat which takes up more space, and the other individual having more lean muscle tissue which proportionately takes up less space, then the person with a higher fat to lean mass ratio will take up more space, thus the larger dress size.

Example 1:

Example 2:

So it is clear from these images of real women that a woman can be the same height and the same weight, but look COMPLETELY DIFFERENT.  This is because the components of what is making up this weight has changed.  A lady with less fat, and more lean muscle tissue can actually look smaller (due to the muscle taking up less space) but be exactly the same weight.  As you can see from the both images, the lady has significantly more lean muscle mass than in the before photo, however they are actually lighter and slightly smaller/leaner.  This is simply due to everything we have mentioned above, more muscle tissue which takes up less space and less fat tissue which takes up more space. The result is a leaner, smaller body at the same weight.

Resistance training is perhaps the best way we know to help improve your body fat ratio more towards having lean muscle tissue and less body fat.  Women often fear getting "bulky" with resistance training however due to having much less of male hormone testosterone, and for the reasons we've explained above about muscle taking up less space than fat, that this is generally a fear without merit.  Aside from the health issues and the obvious aesthetic benefits, women especially should be exposed to more resistance training to help address issues with bone density (Especially as they get older).  Resistance training has also been shown to be as effective at reducing issues related to metabolic syndromes like diabetes, just as much as aerobic training (1) Resistance training also be extremely effective against the common health improvements associated with Aerobic training like reduction in cardiovascular disease, cancers and practically every chronic disease you know of. It's also an effective method, combined with a sound nutritional plan of course with getting leaner and weight management (2,3)

 I'd argue resistance training is perhaps one of the healthiest practices you can do, not just for your body but also for your psychological health. Yes, resistance training can also be excellent for your brain.

👉🏽 If you'd like to try this fabulous method of training and a plan to introduce you safely into resistance training, then try our online memberships for free by clicking here! 👈🏽



  1. Association of Resistance Exercise, Independent of and Combined With Aerobic Exercise, With the Incidence of Metabolic Syndrome (PDF Download Available)
  2. Diabetes Care
  1. https://synapse.koreamed.org/DOIx.php?id=10.4162/nrp.2010.4.4.259&vmode=FULL
  1. Exercise and cognition in older adults: is there a role for resistance training programmes?
Cecilia Harris
Founder & Head PT

Cecilia is the co-founder of Results with Lucy and face of Results with Cecilia.

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  • Lorna September 19, 2019

    It’s so hard not to pay attention to the scales when I KNOW I have fat to lose so this has been really helpful, thank you x

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