wallpaper resolution

When I use a downloaded wallpaper for my desktop and install it, it is not real sharp in detail.what is best resolution to use for this purpose?
Any help or suggestions greatfully received. Van

The native resolution of your monitor.

Regards.

I have a 20" iMac ,what is the native resolution?

1680 x 1050 so download pictures at that size if possible (Or bigger ones which will scale down as long as they are in same width/height ratio)

Wallpaper resolution

Thanks for the replies, I've made a note to do that in the future. Van

make sure that when you are visiting a wallpaper website, you are actually downloading the picture. If you just drag the preview of the wallpaper to your desktop and then set it, the resolution will be way to small