My primary carry of choice is a G23 with a spare magazine on the side of the mag and I tuck it in the small of my back and it disappears even with the $20 holster I've got, even with just a looser tshirt and standard jeans. I'm not a big man either, I'm pretty skinny so it I don't have a lot of space on the side for it.
My brother buys nicer holsters, and he tucks a full size Sig 1911 under any tshirt he's wearing. On the same note, I've tucked a 1911 in back, but I need an extra loose tshirt to pull of a 1911, at least with the holsters I have.
Basically, a good belt and pants, even if they're not made for carry, negates the weight of a gun. I could nearly forget I had the gun with me, and I've had to feel to see if I've got it when I've been sitting around playing Xbox for too long (I have the bad habit of taking it out and setting it beside me when doing so, so I always have to check to make sure I've got it before I move elsewhere in my home).