[MnWhoHBreasts]

Here's a UK size chart which gives an idea for understanding cup sizes. It has to be noted once again that the cup letters are not something universal, they're nothing but a ratio of cup volume to band lenght. Also breast shape is a big factor on how breasts look like and how bras fit, what fits by measuring tape might not be what actually fits the best and very often cup is shaped wrong, its too deep or too shallow, wire width doesn't sit in right place. Bra should be like good shoes, made fot the wearer.



Here's a quick conversion table to understand the differences of most common sizing systems.


Idea about breast shapes, note that width and shape of the chest behind makes a lot of difference, this one shows what different root widths do to the shape.
 

This doesn't go through chest shapes, a lot of trans women and men have wide chests, so east-west shapes are common, with wide root that makes breasts look much smaller than they actually are. That's a thing with wide roots almost always except when they're also very projected which is a rare combination. Then there's different fullness in shape which is yet another factor on on proportions.

Most guys will never be clocked as having anything else than moobs or pecs, even if they're quite big. Especially on a chubby dude, they will never register unless they're huge which is likely to never happen. But a slimmer guy with narrow chest and very round and full shape will have harder time trying to fly under the radar.

When I was still hiding my transition and wearing 80F (EU) bra, no one had faintest idea of anything. That's quite a bit of boob already, but taking in consideration my height, size and breast shape, its no wonder. I think the point of no return is when they're as wide as your face, stick out from below any clothing and have obviously round full shape. And wider than chest from front is something no man ever has. Cleavage is of course super mega obvious tell.

Nicely said and thank you for the information. Guys do have a wider set than most woman and will never have any cleavage, at least what would look normal. Bigger guys do hide it better if that is what they want to do.

[Heaven's Night]

Yes, but also keep in mind that chest shapes and widths aren't easily determined as male/female only as the variance in both sexes could be drawn as an overlapping bellcurve where averages differ to an extent. Also note how this is different depending on ethnicity too and obviously goes over to any physical characteristics, its always like two overlapping bellcurves where average for men and women overlap but slightly differ.

You are correct that men can rarely get a decent cleavage going on, but its not outside of possiblity either. Some dedicated gym rats almost get that with nothing but huge pecs. But I would safely claim that most men can go without much notice while sporting rather large boobs with no effort what so ever. People have such weird way of discerning sex that one characteristics will get ignored if there isn't enough details going to that direction. This is how so many women too get misgendered by accident if they're just androgynous enough for people to make a mistake.

I think guys can keep on growing boobs and not worry much about it, only when it hits a certain point in body proportions and shapes is when it could be problematic. In a similar manner, this is how it will help trans women to cis pass easier. Body proportions are rarely talked about, but in my experience, it is a huge advantage to be curvy enough. I have never been super masculine, but my height and over all size is above average women, I felt that once I hit a certain point of having obvious hourglass/figure 8 shape and big enough boobs for my frame, that's when people started automatically registering me for a woman at all times.

Magic of perception, its more like an art than science as people do it in a weird way.

[MnWhoHBreasts]

Very true....

[olgaitsuka]

Unless you're practically naked (including semi-naked), boobs can easily be hidden, regardless of size.
Women all over Asia do this all the time to appear more child-like, even those who have really large boobs succeed in hiding it.
But one thing that is notable straight away is your face, and it's something hormones alone can't change.
They can if you take estrogen and cut your nuts off at the age of 9, but not if you're already an adult.

My boobs really small, but they do get exposed if the strap of my laptop bag ends up between by breasts, even if I wear a thick jacket.
Some other feminine features get exposed by the bag itself, since you wear it on the side of your body, so you can see a notably smaller waist to hip ratio.
So I ended up wearing a backpack instead.

Best way out is to just not care about what others think, but I still feel a bit awkward when these things happen.

[Heaven's Night]

Big enough can't be totally hidden. If I were something baggy, I just look fat, but there's no way to not see that there's something on my chest.

And HRT can definitely change face a LOT, even bone structure because it changes every soft tissue there is, including what keeps our faces together and it also redoes bones, albeit much slower than everything else.

I will note out every HRT myth being spread, its not as bad what people claim and "late" start does not mean it isn't effective.

[MnWhoHBreasts]

True, depending on the size of your breasts, but even if a baggie shirts makes you look fat, they are hidden a bit but understand where you are coming from.