How do I find out screen resolution of my Linux desktop?

It refers to the clarity of an image on screen. Screen resolution suggests the number of dots or pixels on the entire computer screen. For example, when you say a 640 x 480 screen resolution then all you means is individual 640 dots on each 480 lines i.e. 307K pixels.

Use xdpyinfo command to find out current screen resolution:

$ xdpyinfo  | grep 'dimensions:'

dimensions: 800×600 pixels (283×212 millimeters)

You can also use xrandr command:

$ xrandr | grep '*'

*0 1024 x 768 ( 283mm x 212mm ) *61

You can also use Desktop tools to find out current desktop screen resolution:

(A) Gnome Desktop

Click Gnome Desktop menu > Preferences > Screen resolution

(B) KDE Desktop

1. Click on K desktop Icon > Select Control Center
2. Select Peripherals (under Index tab) > Select Display
3. It will display Screen resolution or size

See Screen resolution at wikipedia.