Which file size?
 

What on average would a full mp3 album size be if i were to search.

I ask this cause i downloaded what i thought was a full album but it wasn't, so i was just wondering what the file size should be before i download.

That really depends on the type of album and the bitrate used. I've downloaded complete albums with sizes ranging from around 45MB anywhere to 90MB. Anything less than 40MB is probably either not an entire album or it's going to be so poor of a quality it wouldn't be worth messing with.