What is the optimal size of product images both large and thumbnail?

I wouldn't make your main product image any larger than 300 pixels wide. The thumbs should be around 75 pixels wide.

I agree... much bigger then that, and you'll push your cart off to the side. Nobody likes to use those horizontal scroll bars!

As for the full size we try to keep it under 300px wide. However, it depends on your site settings for your thumbs. We display 3 across and found 100x100 px for thumbs is good. 4 across would probably need 75x75.

I would recommend that you keep the width and height the same on all thumbs for best results. Also I would definately test various sizes before you begin. You don't want to size all your product images to 125x125 and then find out it's too big and need to resize down to 75x100.

I am using 3 across @ 100X100 and on the bigger image 300X300. For me I think this shows the most detail of each product.

I have also used 200X200 that was a little too small @ 1024 X 768 res.

CBHALE

I agree. I use 300 X 300 for the full size, and 100 X 100 for the thumbnails. I am using three across as well. I think this is the best size for using three across, since it will give decent detail without stretching the screen.

I use 4 accross with 100x100. I don't think it looks TOO cramed . But I would prefer to go 3 accross 100x100. Much smaller of a thumb makes it too hard to see...or maybe I'm blind...