That's about what mine are. The old, built in place ones were 12" inside, now they are 12" on the outside. After we redid the kitchen, I was putting plates away and they no longer fit. I was so mad. I started going around to all the manufacturers with a tape measure to see if I'd gotten screwed.

Some are even worse. If the back of the cabinet is thick, you lose even more interior space. :(

Mine are about 11 1/2" on the inside, with the exception of one that sits on the counter and is about 14 1/2" deep. It's my favourite cabinet and holds all my plates, bowls, etc. What was interesting about this cab is the KD called for a "regular depth" cabinet that was pulled forward creating 3 inches of dead space behind the cabinet. Sure glad I caught that one!
I'm putting together my must haves for my new kitchen and one of the first things on the list is deeper uppers (and more drawers).
My friend is a cabinet maker and he said that his standard uppers are 13".

Ha ha, I saw "Death of upper cabs" I will probably put shelves or just hangers in my heavy work zones.

My existing uppers are 12" and things still get lost in the back, especially on the top shelves.

Generally, "standard" cabinets are 12" on the exterior dimension - this is done because boards used to make cabinets are in 48" widths...so, you can get 2 bottom cabinet sides or 4 upper cabinet sides from a board. If they made them "standard" at 13" (or whatever), they would only be able to get 3 upper cabinet sides and then have leftover board.

So, when they have them as 12" and then put the back on them, it reduces the interior dimension to 11-something-ish inches.

We opted for 14" deep cabinets when we had ours made. It has worked out fantastic - extremely happy with the additional depth.

Rmtdoug - I keep reading this as " death of upper cabinets" too! Haha. I thought it was going to be about how open shelving is bringing about the death of upper cabinets. I could see that post in the near future. :)