On an Android phone the wallpaper spans across all of the home screens.
So what size should pictures be to fit properly as custom wallpapers?
Android Enthusiasts Stack Exchange is a question and answer site for enthusiasts and power users of the Android operating system. It only takes a minute to sign up.Sign up to join this community
Here are the correct wallpaper dimensions for the phones cited in Leimi's answer:
If you device isn't listed there is an easy way to figure out the dimensions of the wallpaper based on your particular phones resolution:
so for example my Moto Droid has a screen resolution of 480x854 so I want my wallpaper to be 2x the width (480 pixels) and 1x the height (854 pixels) = 960x854.
Here is a chart with most devices specs to help find the resolution.
Also check out this Lifehacker article that explains Android wallpaper sizing well.
It depends on your screen resolution :
edit : in fact some of this dimensions work but are not the correct ones (they fit because of the same aspect ratio). Matt's answer is better !
I think you shouldnt look at resolutions, but aspect ratio.
Resolutions are device-specific, but all devices, regarding their screen resolution use the same aspect ratio for scrollable wallpaper.
As I recall, the ratio is 5:4, because this aspect is good for having a wallpaper that scrolls a bit while you scroll through your homescreens.
Its been a while since I got that info so something might have changed, but as long as you keep that ratio (and the resolution higher than your devices resolution) you will have a nice crispy-clear image.