The tiles are just under 1 ft square, so you could do roughly 2' x 6', 3' x 4', etc.
I find generally find that 6 tiles on the table is enough, but keep extras on hand in case I have something pre-drawn or I want to replace tiles without erasing something I've already drawn.
This is great if you have a "rolling battlefield", where the PCs might run off across several tiles, then come back.
Tact-Tiles are really great in chase situations too, where you can rotate the tiles under the PCs like a treadmill.
As they advance across the tiles, you just pick up the ones behind them, erase, and put them in front of them again.Also, something that rarely gets mentions, but that I think is awesome, is the fact that the tiles are thick and rigid enough to allow you to slide the entire play surface around the table without disrupting the minis. That's something you can't do with a battle mat, and I find it to be very handy. Instead of a player having to get up and walk around the table to move his mini, we just slide the tiles over to him. For that matter, during our last game, we actually rotated the tile set mid-game, because the flow of the action changed.
