Below, the most common monitor formats and ratios I know of and create desktop wallpaper graphics for are listed for your reference...

(3:2) 1152x768, 1280x854, 1440x960

(4:3) 768x576, 800x600, 1024x768, 1280x960, 1400x1050, 1600x1200, 1920x1440, 2048x1536

(5:3) 800x480, 1280x768

(5:4) 1280x1024, 2560x2048

(8:5) 1280x800, 1440x900, 1680x1050, 1920x1200, 2560x1600

(16:9) 854x480, 1280x720, 1366x768, 1920x1080

(17:9) 2048x1080

Dual monitor: 3200x1200, 2560x1024, 2048x768