What sized 2d artwork for mobile device?

I’m planning on making a 2d platform game using Smooth Moves. I have an artist on board who will be using Photoshop to draw the assets.

What size should I require them to be drawn? I was thinking of getting them draw bigger than needed and scale them down, but I don’t even know what size to scale them down to? There’s going to be a lot of artwork in this, so I really want to ensure the size will maximise the quality.

Any suggestions please?

it depends of the devices you are targeting . for example retina display on ipad 4 and 800 X 480 display has biiig difference , so this is very noob question . Best is to make them suit to the biggest screen and than resize to the smallest . Best of the best is to make them vector .

If you are doing a 2d game, get your artist to use illustrator and have all your original art in vector .ai format. You can still place psd files etc for a more textured look. This way you can export the vectors to bitmaps at any resolution you want later with no loss of quality. If next year apple bring out a 4k x 2k device, it’s easy to just re export at the higher size.