clear pictures 640 or 800 size?

[funkyclassicsboutique]

Hi,

I know this sounds dumb. But, I can't remember what size I have been using for pictures. Some of them look blurry to me in my listings.

It took me a while to figure out the adobe mass uploading feature, which was a huge help. But, should I upload in 640 or 800.

Thanks for your help. Lisa