You'll have to look at your sprocket, it's stamped. Most I've seen is 3/8-7 stock on 46's, but that might just be a local dealer thing, too.
If you're running a 20" on a modded 46, you've got plenty of power left over to gear up the chain drive to an 8 pin sprocket. But depending on your bar, and how much you've stretched your chain, you may need to add a link to get it to fit. I'd run the 7 until you're ready for a chain, then the sprocket rim is @ $4, and get your chain with 73 drivers instead of 72. Its a simple E-clip to swap sprockets, if needed for the big bar and hard wood.
Assuming you're using a rim sprocket setup, and not spur of course.
-Ralph