How to Check COM Ports in Windows 11

To check COM ports in Windows 11, right-click Start and select Device Manager. Expand Ports (COM & LPT). Each serial device is listed with its port number in brackets, such as USB Serial Device (COM4). Use that COM number in the app or tool that talks to the device.

Applies to: Windows 11. Checked on September 24, 2026.

What a COM port is

A COM port is a serial connection. Most PCs no longer have a physical serial port, so COM ports today usually come from USB devices: USB-to-serial adapters, Arduino and other development boards, barcode scanners, GPS receivers, 3D printers, and lab or networking equipment. Windows gives each one a number, such as COM3, and apps use that number to connect.

Find the COM port in Device Manager

1. Plug in the serial device or USB-to-serial adapter.
2. Right-click Start (or press Windows + X) and select Device Manager.
3. Expand Ports (COM & LPT).
4. Note the COM number shown after your device’s name.

Not sure which entry is yours? Unplug the device and watch which line disappears, then plug it back in. Windows usually keeps the same number for the same device in the same USB port.

See how to get to Device Manager in Windows 11.

List COM ports with a command

• PowerShell (names and numbers): right-click Start, select Terminal, and run Get-PnpDevice -Class Ports -PresentOnly. The FriendlyName column shows each device with its COM number.
• PowerShell (numbers only): run [System.IO.Ports.SerialPort]::GetPortNames() to list every COM port in use, such as COM1 and COM4.
• Command Prompt: type mode and press Enter. It shows the status and speed of each available COM port.

Change a device’s COM number

Some older programs only work with low port numbers, such as COM1 to COM4.

1. In Device Manager, right-click the device under Ports (COM & LPT) and select Properties.
2. Select the Port Settings tab, then Advanced.
3. Choose a new number from COM Port Number and select OK.

4. Unplug and reconnect the device, then check the new number in Device Manager.

If Windows says the number is in use, it may be reserved by a device that isn’t plugged in. See the next section to free it.

Free up COM numbers used by old devices

1. In Device Manager, select View > Show hidden devices.
2. Expand Ports (COM & LPT). Greyed-out entries are devices that aren’t connected.
3. Right-click an old entry you no longer use and select Uninstall device.

Only remove entries you recognize, such as an adapter you’ve thrown away.

Check the port speed and settings

On the Port Settings tab of the device’s Properties, you can see and change Bits per second, Data bits, Parity, Stop bits, and Flow control. They must match your device. Many apps set these themselves, so check the device’s manual before changing them.

If Ports (COM & LPT) is missing

• Show hidden devices from the View menu.
• Look under Other devices for an entry with a yellow warning sign. It usually needs a driver from the adapter or board maker’s website.
• Try another USB cable. Some cables only charge and don’t carry data.
• Try another USB port, preferably one directly on the PC rather than a hub.
• Check Windows Update in Settings > Windows Update > Advanced options > Optional updates for a driver.

Frequently asked questions

Why does my device’s COM number keep changing?

Windows can give a new number when you use a different USB port. Plug the device into the same port each time, or set a fixed number as shown above.

How do I check open network ports instead?

Network ports are different from COM ports. See how to open ports on Windows 11.

Can two apps use the same COM port at once?

No. Close the other app first, or you’ll get an “access denied” or “port in use” error.

To check USB ports instead, see how to check USB ports on Windows 11. More help is on our Devices & Drivers Help & Guides page.

Matt Jacobs

Matt Jacobs has been working as an IT consultant for small businesses since receiving his Master’s degree in 2003. While he still does some consulting work, his primary focus now is on creating technology support content for SupportYourTech.com.

His work can be found on many websites and focuses on topics such as Microsoft Office, Apple devices, Android devices, Photoshop, and more.