Window Placement

Window Placement is a lightweight piece of software you can use to find out some simple information about your display devices, including the size of your virtual desktop.
It's available via a command-line interface and doesn't have any arguments, so it can be used even by those with little or no experience in console-based utilities.

Doesn't need installation

It's not necessary to go through a setup operation, thanks to the fact that Window Placement is portable. You can extract the files from the downloaded package and place them anywhere on the disk or copy them to a thumb drive to effortlessly run the tool on any computer without setup.
Unlike most installers, this program doesn't add new entries to the system registry or generate additional files.

View monitor information, such as dimensions

You can call its process from a Command Prompt dialog or any other preferred application that runs the console environment, and specify the file's name and extension.
After hitting the Enter key, the utility instantly scans your PC and retrieves monitor information, showing the descriptions of all your display devices, which one is set as primary and which is the work area, along with the width and height of each monitor.

Doesn't show more useful device info

Unfortunately, there is no command available for dumping all this information to file. Instead, you can select it with your mouse and press Enter to copy it to the Clipboard. The text can be then pasted in a text editor and saved as a document.
This is where Window Placement's functionality ends. Sadly, it doesn't show in-depth information about monitors, such as driver details. Nevertheless, it can still be used for finding out monitor sizes. It had minimal impact on the computer's performance in our tests and instantly revealed monitor data.