Ink levels can usually be checked from the screen on the printer itself if the printer has a screen prompt that shows visuals of ink levels. Ink levels can also be checked from the computer the printer is connected to.
To check ink levels from a Windows computer, click on the start menu from the computer's home page and then click Devices and Printers. From Devices and Printers, click on Printer, and then check the ink levels if the printer's software is designed to show ink level statuses.
To check the ink levels on a Macintosh computer, go to the Applications folder and click System Preferences, and then go to Print & Fax and click on the printer's icon. Click the Options menu and then Options & Supplies. Then click on the Supply Levels tab to check the printer's ink levels.
Note that warning messages from a printer do not necessarily mean that the printer is completely out of ink or that the ink needs to be replaced right away. Blurry, incomplete or faded prints are a good sign the ink is low, although this is typically an inconvenient way to find out that the computer is low on ink.