How to know your bodyfat percentage using the mirror as a skinny or skinny-fat guy

The Skinny Guy’s Guide to Body-Fat Percentage

As a skinny guy, it can be hard to figure out what your body-fat percentage is. Here’s why: let’s take a totally average guy in this study. He goes to get a DEXA scan, and he’s told that he has a body-fat percentage of 20%. Then he goes to sit in the BodPod, which puts him at 22%. A bit of a discrepancy, but he can be reasonably confident that he’s between 20–22%. Moreover, both of those body-fat percentages have the same implication for his health and appearance: he’s a decently healthy guy who looks a bit out of shape.

The overweight guy goes in next. DEXA puts him at 34%. BodPod puts him at 32%. Now it’s DEXA that’s estimating high, but the discrepancy is still just 2%. Again, not a big difference at all. He’s overweight either way, and he could stand to lose some fat.

Now you walk in. DEXA puts you at 9%. Amazing! Not only are you lean enough to bulk aggressively, but you’re also leaner than most professional athletes. Next, you get your BodPod done. It tells you you’re 22% body fat…

Huh? 22%? That’s not the end of the world, but you’re slightly outside of the healthy body-fat percentage range. You’re skinny-fat, you might say. And so you might want to start with a cut before bulking.

You’ve spent a few hundred dollars and an entire day getting two of the most accurate body-fat percentage tests in the world, and you can’t even tell if you should be bulking or cutting. For guys who are underweight, DEXA and BodPod can be off by up to 13%. Totally useless.

So in this article, we cover why your body-fat percentage matters even as a so-called “ectomorph,” how to measure it properly, and then we’ll run through some real-life examples (with pictures) so that you have a better idea of how to judge your leanness at a glance.

Illustration of a skinny ectomorph building muscle and becoming muscular.

15% Body Fat Marks a Turning Point—Sort Of

When we’re under 10% body fat, our deflated fat cells are hungry, our levels of cortisol rise, and our testosterone plummets (study), making it harder to build muscle, let alone build muscle leanly. And so if we focus on trying to stay at very low body-fat percentages, we’ll build muscle very slowly. This gets more and more extreme as our body-fat percentage gets lower, so building muscle at 9% is a lot easier than building muscle at 5%. That’s why the healthy body-fat percentage range starts at around 8–12%, depending on the person (study).

For example, when a bodybuilder steps off the stage and gets back to eating a regular amount, he’ll often gain 10–20 pounds of pure fat. And that’s actually a good thing. He isn’t gaining fat because he’s doing anything wrong, it’s simply that his body needs fat more than it needs muscle. Then, as he gets closer to 10% body fat, he can start building muscle properly again.

Also keep in mind that if we cut down much further than 10%, it’s not only worse for our health, it can also make us look less healthy. Muscles look good when we’re lean, but we don’t have many muscles on our face, so at low body-fat percentages, our faces can start to look quite gaunt. As a result, for the sake of our performance, general health, appearance, and ability to build muscle, it’s usually a good idea to let our body-fat percentage drift to 10% or higher.

When we’re over 15% body fat, some experts believe that our inflated fat cells can start to interfere with your overall insulin sensitivity. If that’s true, then even a great weightlifting routine wouldn’t be able to get our muscle fibres quite as insulin sensitive, and even a good muscle-building diet wouldn’t be able to spark quite as much muscle-protein synthesis. However, most research looking into the hormonal effects of various body-fat percentages only detects an effect when guys get over 20% body fat (study, study). So it could be that these changes don’t really start to manifest at 15%. Even so, this effect gets more pronounced as our body-fat percentages get higher, so bulking at 17% is certainly a lot easier than bulking at 30% (study).

This may be why so many skinny-fat guys are unable to bulk leanly. When we gain weight, it seems to be mostly fat. So we cut away the fat until we’re back down to 20%, and then we try bulking up again, and again we just get fatter. So we give up, thinking that our genetics suck.

Our genetics don’t suck, though. We’re just not lean enough to bulk properly. We should be reducing our body-fat percentages a bit before trying to bulk up. Here’s how that works: what to do if you’re tired of being skinny-fat.

Note: being over 15% body fat doesn’t mean we’re fat. The average healthy guy has 20% body fat. It just so happens that when we’re trying to build muscle, it may be better to be on the leaner side of healthy.

When we’re in that golden zone of 10–15% body fat, our fat cells are satiated enough that our insulin sensitivity drops. But they aren’t so full that they start messing with our hormones, either. We have optimal cortisol and testosterone production and great insulin sensitivity (study). So when we start following a good bulking program, the insulin sensitivity in our muscle cells will skyrocket. If we feed ourselves a good muscle-building diet, then our muscle fibres will grow and our fat cells will not (or at least not as much).

For example, here’s Taylor gaining 20 pounds while staying between 10–15% body fat.

He’s gaining over a pound per week but he’s hardly gaining any fat. And he’s just doing three workouts per week, each lasting about an hour. No crazy supplements or anything wild, just a solid science-based approach to building muscle. This is why it’s so important to be able to guesstimate our body-fat percentages. It doesn’t matter if we’re a few points off, but we need to know whether our body-fat percentages are in the cutting or bulking range.

Getting under 15% body fat is important visually as well. That’s when we start to look like we’re in good shape. It’s not enough to impress other men, but it’s when we start to look optimally attractive to women. Some women do prefer chiseled abs, but the research pretty clearly shows that most guys have fairly optimal attractiveness by the time they get down to 15% body fat. This will not only give us great muscle definition, but it will also make our faces look lean and healthy.

The other thing to keep in mind about our abs is that we don’t just need to cut down to a low body-fat percentage, we also need to bulk up our abs. Most overweight people naturally have bigger muscles, including their ab muscles. For them, getting lean will yield great ab definition. However, for us naturally skinny guys, our abs are often skinny. We need to bulk them up in order to see them properly. So getting overly lean before bulking up our abs often doesn’t work very well.

Still, if you’re much over 15% body fat, the quickest way to make yourself more attractive is to trim off a few body-fat percentage points. This is true even for skinny guys. If you haven’t built much muscle yet, a good muscle-building program combined with a good cutting diet should allow you to gain a few pounds of muscle even while you lose fat.

Then when you get down to 10–15% body fat, the best way to become more attractive is to focus on building muscle—on bulking up. And since your muscle cells will be more insulin sensitive, you’ll be able to build muscle more leanly (examples coming). This is all to say that we need a somewhat precise way to determine whether we’re under 15% body fat or not.

How to Estimate Your Body-Fat Percentage

We’ve already covered why DEXA scans and BodPods won’t work properly until you’ve already bulked up to a solid weight.

Bioelectrical Impedance Analysis (BIA scales)

Are bioelectrical impedance analysis scales (BIA) an accurate way of measuring body-fat percentage? No, BIA scalres are cheap and convenient—most modern bathroom scales have this feature—but they’re even less accurate than DEXA and BodPod. Again, they’re just not something designed for guys like us. They’re for tracking fat loss in overweight people, not muscle gain in skinny guys.

To give you an example of how bad BIA scales can be, when I was bulking up from 130 to 170 pounds, it told me that my body-fat percentage had climbed from 10% up to 20%. This made me sad, but I tried my best to ignore it because my abs looked the same as they always did. Then something strange happened when I made it up to 185 pounds. It determined that I had an “athletic” body composition, so it switched to using a different algorithm. Instead of 20% body fat, it started saying I was 8.5% body fat.

The Navy’s Measuring Tape Method

Is measuring our waist circumference, as the Navy does, a good way of estimating our body-fat percentage? Yes, it can be, especially for general health purposes—a large waist circumference can indicate visceral fat storage, which is bad for our health (studystudystudy). But again, this way of measuring body-fat percentage used to determine whether a guy is overweight or not. Plus, it reads abdominal muscle gain the same as it reads visceral fat gain. Bigger ab and lower back muscles will increase your waist measurement, after all.

Skinfold Calipers

Skinfold calipers can be quite useful. They aren’t good at estimating our body-fat percentage, but they’re quite good at measuring whether we’re gaining fat or not. That can be quite handy while bulking.

The main downside is that they require a decent amount of training to use properly. Otherwise, they don’t measure body-fat percentage well enough to be that helpful. Still, they’re affordable, you can use them from the comfort of your own home, and they can work well if you can learn to have a skillful hand. Not bad at all, and the best method so far.

The Mirror Method

Can we estimate our body-fat percentage simply by looking at ourselves in the mirror? Not perfectly, no, but it’s very easy, and it might be good enough. Assuming you already have a mirror, this method is free. It’s also easy. And so long as you’re between 9–15% body fat, it’s actually quite accurate. Unlike the other methods, this is a method that works better the more muscle definition you have. So it works well when you’re thin, and then even better as you gain muscle.

Moreover, if you’re over 15% body fat, you know you should be cutting anyway. So even when the mirror is inaccurate, it’s still accurate enough to tell you that you should be cutting.

Now, you might be thinking, if you’re cutting, won’t you want to track your body-fat percentage to make sure that it’s going down? Actually, no. There are better ways to track your cutting progress. After all, you should always be following a good weightlifting program while cutting. Obese guys will lose mostly fat when they lose weight, but us naturally skinny guys, ectomorphs, are more prone to losing muscle. Not because we have worse genetics, just because we have less fat to lose, and so when we lose weight, we can’t pull all of that energy from our fat stores. And since we don’t have any muscle to spare, lifting weights while losing weight is mandatory.

So, since we’re lifting weights anyway, you can just make sure that you aren’t getting weaker. If you’re maintaining or gaining strength, you aren’t losing muscle.

To track how much fat you’re losing, you should weigh yourself each week while cutting. If you aren’t losing 1–2 pounds each week, you need to adjust your calorie deficit. This is how you ensure that you’re steadily losing fat.

So all you need to do while cutting is monitor your strength in the gym, monitor your weight on the scale, and then check how you’re looking in the mirror. This means that even while cutting, the mirror works pretty well as your primary way of tracking your body-fat percentage.

Thing is, to use the mirror, you need to know what you look like at different body-fat percentages. In theory, that’s easy enough. You can just look up a photo of people at various body-fat percentages. Problem is, most of those comparisons are useless for us ectomorphs. Here’s a good example of a chart that doesn’t help us:

This Nerd Fitness chart is actually a whole lot better than most, but I chose it because I like Nerd Fitness, and because Steve Kamb makes this same point in his article Everything You Need to Know About Body-Fat Percentage: muscle mass has a huge impact on how lean you look.

I couldn’t agree with him more. Let me show you why. Here’s GK’s progress over the course of The Bony to Beastly Program. He managed to stay at around 10% body fat the entire way through, but you can see that he started the program with almost no muscle definition, and finished the program looking totally chiseled. This has nothing to do with fat, everything to do with muscle.

So when you get a chart with random variance in muscle mass, it’s impossible to compare body-fat percentage. We can see someone’s muscle definition changing, yes, but we have no way to tell whether that’s due to varying degrees of muscle mass or body fat.

There are other problems with this type of chart:

  • The guys have varying tans. How dark your skin is has a huge impact on how lean you look. That’s why the bodybuilder has such an exaggerated spray tan.
  • Some guys are oiled up. Again, this is a trick used to make guys look leaner.
  • Some guys pumped up their muscles for the photo. Another trick used to bring out vascularity and muscle definition, making guys look leaner.
  • They’re different guys. One guy might have proportionally bigger ab muscles, another might have different body fat storage patterns, some will have different amounts of visceral versus subcutaneous fat.

Moreover, the lighting isn’t the same. For an example of why that matters so much, take a look at Omar’s progress pictures. Like GK, he’s at roughly 10% body fat before and after bulking up.

On the left, he’s at the beach and there’s a lot of ambient lighting. He has abs, but you can only just barely see them. On the right, you can see that he’s gained a ton of size in his chest, traps, shoulders and arms, but is he also leaner? It’s impossible to tell because the lighting is so different.

Generally, overhead lighting will make you look more muscular than ambient lighting. This is why you probably look leaner in your bathroom mirror than you do on the beach (depending on the weather).

It’s even harder for us ectomorphs because so few examples show us skinny guys at varying body-fat percentages.

So we’ve got two charts:

  1. An ectomorph who hasn’t bulked up yet.
  2. An ectomorph who’s successfully built a good amount of muscle mass.

And we’ve used illustrations so that we can keep all the variables constant except for body fat.

Here’s how you use the body-fat percentage charts:

  1. Find a mirror
  2. Turn on some flattering overhead lighting (bathrooms work well)
  3. Flex your abs and your butt (to rotate your hips into a decent position)
  4. Compare your abs and muscle definition to these charts

Here’s what 9–20% body fat looks like on the typical skinny guy:

Here’s what 9–20% body fat looks like on a skinny guy after he’s bulked up:

Real-Life Body-Fat Percentage Examples

Here’s me at 11% as measured by DEXA scan and 10% as measured by BodPod. Note that I’ve bulked up to a bodyweight of 185 here (BMI of 24) so I’m heavy enough for these methods to be fairly accurate.

Here’s what that looks like in video, and with less flattering lighting. As you can see, I look the most like the 12% illustration shown above.

If you want to see what that ideal 10–15% range looks like, here are some bulking transformations of guys doing our Bony to Beastly Bulking Program. I’ll also give some examples of guys bulking at slightly under 10%, or slightly over 15%. That should give you a good idea of what it looks like to have a body-fat percentage that’s ideal for bulking.

I’ll give my guesses for what their body-fat percentages are both before and after, but keep in mind that the big distinction we’re trying to make is whether they’re lean enough to be bulking.

Here’s a great example of bulking at a very lean body-fat percentage. EddiB is only just halfway through the program now, and he’s still going strong, but so far it looks like his body-fat percentage is ever-so-slowly climbing up from around 7% as he goes.

What’s great about this is that even if he gains a few more pounds of fat as he continues bulking, he should be able to finish his bulk at an ideally lean body-fat percentage.

Here’s a good example of starting at a very lean body-fat percentage. JonKyp went from something like 7% up to what looks more like 10%. This is a good example of faces looking great at around 10% body fat.

Here’s Nick starting at what must be around 8% body fat. He’s quite lean after gaining 27 pounds, but I’d guess he’s climbed up to around 11% by the end.

Here’s Albert starting and finishing at around 10%. You can see that his muscle definition goes way up as he bulks, even though he probably gained something like 2.5 pounds of fat to maintain his body-fat percentage at 10%.

Lucas gained a bunch of muscle definition as he bulked up, but he’s probably at around 12% both before and after. He’s still at the lower end of the range, so he could just keep right on bulking without any issue.

Here’s Ash gaining a couple percentage points as he bulks, but winding up looking better for it. Looks like around 10% to start, more like 13% at the end.

I’m guessing Patrick was around 11% starting out and around 15% at the end of his 40-pound bulk. At this point, he might want to cut off a few pounds before bulking up more, but he wouldn’t have to—he’s still just barely lean enough at the end.

Here’s JoeBrusk, who started with way more muscle. He was probably at around 15% at the beginning (which is lean enough to look optimally attractive to women), but after some body recomposition, he finished at around 10% (which is lean enough to look impressively badass to other dudes).

John L started out with a good amount of muscle, and at around 14%, I’d guess. He finished at around 15%, I’d say, given that his muscles have about the same amount of definition despite being quite a big larger.

Here’s Hugo starting and around 11% and finishing at around 14%. What’s cool about this one is that he’s gained such an incredible amount of muscle that he’s got way better muscle definition despite being a few body-fat percentage points higher.

Here’s a good example of bulking up at the upper limit of that ideal bulking range. I’m thinking Josua is flirting with 16–17%. This has him starting off with little definition, but finishing looking like some sort of professional football player.

I normally use my 130–185lbs bulking transformation, but here’s me at 200lbs cutting down to 180lbs. I started the cut at around 20% body fat and finished at around 10%.

Klaus is a good example of someone who came in at around 20% body fat. He was able to transform his physique by alternating between cutting and bulking, finishing 22 pounds heavier at around 9–10% body fat. What’s so amazing about this is how radically his overall body shape has changed. He’s got a pronounced v-taper by the end of it.


If you’re under 15% body fat, the best way to improve your physique is to bulk up, and the good news is that you should be able to build muscle quite quickly. A beginner can gain 1–2 pounds per week, eventually slowing down to gain around 0.5–1 pound per week. You can expect to gain at least 20 pounds in 3–5 months.

Illustration of a skinny ectomorph gaining muscle and bulking up.

If you’re over 15% body fat, the best way to improve your physique is to cut. If you’re still fairly skinny, you should be able to build a decent amount of muscle even while losing weight overall. Over the course of the next 3 months you could expect to lose 20 pounds of fat while gaining a few pounds of muscle. That will already have a dramatic impact on your physique, and then when you transition to bulking, you should be able to gain around a pound of muscle per week. If you started at 20% body fat, after 8 months (3 months cutting + 5 months bulking) you could expect to be at around 12% body fat with around 20 extra pounds of muscle on your frame.

Illustration showing the Bony to Beastly Bulking Program

If you want more muscle-building information, we have a free bulking newsletter for skinny guys. If you want a full bulking program, including a 5-month workout routine, diet guide, recipe book, and online coaching, check out our Bony to Beastly Bulking Program. Or, if you want an intermediate bulking routine, check out our Outlift Intermediate Bulking Program.

Shane Duquette is the co-founder and creative lead of Outlift, Bony to Beastly, and Bony to Bombshell, and has a degree in design from York University in Toronto, Canada. He's personally gained sixty pounds at 11% body fat and has nine years of experience helping over ten thousand skinny people bulk up.

Marco Walker-Ng is the co-founder and strength coach of Outlift, Bony to Beastly, and Bony to Bombshell, and is a certified trainer (PTS) with a Bachelor's degree in Health Sciences (BHSc) from the University of Ottawa. His specialty is helping people build muscle to improve their strength and general health, with clients including college, professional, and Olympic athletes.