On Windows, right-click the desktop and select Display settings
On Windows, look under Display resolution
On Mac, click the Apple menu and select System Settings
On Mac, open Displays to view the resolution
On Linux, open Display settings or Screen settings
On a browser, use the screen.width and screen.height values in developer tools
On a smartphone, check the Display or Screen settings in the Settings app
On an external monitor, check the monitor’s on-screen display menu
On Windows, press Windows key + I, then go to System > Display
On Mac, hold Option while clicking Scaled in Displays to see more resolutions