Need to know sizes for decals...

Hey guys i want to get some racing #4's for the side of my sled and i am having them custom done and need to know the size to go on the side of my rev.
Also, what is a good size for a sticker to go on the hood...

I am getting a reaper put on the hood but i need to know what size so it takes up a good amount of space but not cluttered and not to close to my headlights... If someone can please help my out with the graphics size numbers that would be great. Having a hard time finding them online.