cover size - epub what's a good size?
 

I want to reduce the size of book cover because it is too large, the Aura it's on displays a zoomed in portion of the cover. Using Calibre I discovered the cover size is 1251x2200, while the Aura's resolution is 1024x768 - no wonder I couldn't view the full cover. As a comparison a kobo touch has an 800x600 screen resolution.

What's a good size? I read somewhere here someone prefers 316 x 450. Most of the novel books I'm just looking at now, seem to have sizes of 299x450

I think the best way to reduce the cover size is to use the readily available paint program within windows. Just copy the original cover and open it in paint and resize to the size you want then save it and upload the new cover to the book.

Now I've never used polish before, and just learned about it, do I need to use that?

Use the Resize Cover plugin ==>> Index of plugins

If you want to edit a cover image, right click the cover in Book Details (right sidebar) and use the Open cover with... option to open it in an external program.

I'll let others advise on optimal size, I suspect it's device/user dependent.

BR

Personally, I go for highest quality/resolution available and just let the reader device or app do the resizing (fit to screen). I'm surprised the Kobo Aura doesn't do that automatically.

The problem is not the resolution of the cover. The problem is the poor coding used to display the cover. Please post the cover XHTML and the relevant CSS so we can see what's going wrong.