I have a problem with scratching on strings (I know its my technique- been playing about a year) so to help me I am going to buy some Elixir strings. However my acoustic guitar was a present and I have no way of knowing what string gauge is on it. The e-store has huge variety of choices - my guitar is a Yamaha FS720S.

Thanks for any help.
I cant say for sure what your guitar would have came with but 12-53 or 12-54 is what acoustics generally come with.