what is the best image size format for imovie iOS

It all depends on what you want to do with the images.

If you don't want to do any moves on the images then make them the exact size of the video.

The iPad 3 edits in full HD, 1920 x 1080.

If you want to do small moves, then make is larger.

But keep the 1920 x 1080 dimensions otherwise iMovie just chops the image to that ratio.

good luck

Yeah 1920 X 1080 is best.

Just watch that iMovie tries to do moves on images.

It kinds of defaults to doing a push in.

And that is why I suggested that you make the images bigger.

So you could make them twice as big, and then you could do small moves in on them.

That looks nicer then still graphics.

Double size is 3840 x 2160.