Kiz,
I also have some Modern Brick styrene sheets from the N Scale Architect. The usable brick portion of the sheet measures in at approximately 9-1/2" x 13-1/2". As pointed out above, you get two sheets per pack, so it should go a long way. I used it on a portion of my A&R enginehouse and have started applying the brick veneer to my SAL station, and I still haven't used up the first sheet.
For scaling purposes, here is some of it applied to an N scale structure that is under constructioh:
Hope this helps,
DFF