Everybody talks about how much terrain we need to play over, the new meta being lots and lots, but nobody seems to agree over how much is enough. I have been thinkin about this and have figured out its easy. You need 2'x3' of terrain to maintain 25% on a 4'x6' board (I think that is the BRB recommendation). I have been basing all of my terrain on 1/8" pcb board and now I have realized that the easiest way to judge terrain is that I need 6 1'x1' pieces and to spread this out cut some of them down to 1'x6" or 6"x6" then you can easily add up your percentage and get to that 2'x3' sweet spot. From there add or subtract 1'x1' chunks to make denser or thinner boards.
6 1'x1' tiles of terrain will field a pretty sparse table (but be completely legal), it is my feeling that the more you cut these 6 pieces down into smaller parts, the better coverage you will have (even though that's not really technically true).
Example 6"x6"
Sooo... You need 4 of these to make 1 1'x1' of your chunk of 6.
I dunno if this is something everybody knows already, but it seems to me an easy way to determine the amount of terrain to play on.