Anyone have an idea of what size 2d background artwork for a platform game should be? Not sure what size to tell my artist. 
platform? mobile? If mobile, you’ll want to break them into chunks.
Yeah mobile but want it future proof as might release for other platforms.
if you generate the 2D background procedurally, you only need to cover some distance from the main camera along the 3rd direction and make the camera follow the player
ok but what pixel size should I tell my artist to draw the art at?
If you’re putting a texture on a plane I believe 1024x1024 is the largest you want to go on mobile, and 512x512 is better, for each chunk/tile. You can make a much larger image and break it into tiles that size.
Do some experiments, ensure you remain around 30mb per level for graphics to be safe.