To check COM ports in Windows 11, right-click Start, open Device Manager and expand Ports (COM & LPT). Each serial device is listed with its port number, such as USB Serial Device (COM3). Unplug and replug the device to see which entry disappears and returns. You can also list ports from PowerShell with [System.IO.Ports.SerialPort]::GetPortNames(), or run mode in Command Prompt.
Quick Answer
Device Manager > Ports (COM & LPT). Change a number in Properties > Port Settings > Advanced.
Steps to Find a COM Port
- Right-click Start and choose Device Manager.
- Expand Ports (COM & LPT).
- Find your device and note the COM number in brackets.
- If Ports isn’t listed, click View > Show hidden devices and check the device is connected and its driver installed.
Other Ways and Tasks
| Task | How |
|---|---|
| List ports in PowerShell | [System.IO.Ports.SerialPort]::GetPortNames() |
| List ports in Command Prompt | mode |
| Change a COM number | Device Properties > Port Settings > Advanced > COM Port Number |
| See port speed settings | Properties > Port Settings |
Troubleshooting
- Device shows under Other devices: Install the maker’s USB-to-serial driver.
- Port “in use”: Close apps that might have it open, such as terminal programs or IDEs.
- Opening Device Manager: See opening Device Manager in Windows 11.
- Network ports instead: See checking if a network port is open.
Frequently Asked Questions
Why does the number change?
Windows may assign a new number when you use a different USB port. Set a fixed number in Advanced settings.
What’s the difference between COM and LPT?
COM ports are serial; LPT ports are legacy parallel printer ports.
Do Bluetooth devices use COM ports?
Some older Bluetooth serial profiles create virtual COM ports, listed in the same section.
Summary
- Open Device Manager.
- Expand Ports (COM & LPT).
- Note the COM number.
- Change it in Advanced settings if needed.
Kermit Matthews is a freelance writer based in Philadelphia, Pennsylvania with more than a decade of experience writing technology guides. He has a Bachelor’s and Master’s degree in Computer Science and has spent much of his professional career in IT management.
He specializes in writing content about iPhones, Android devices, Microsoft Office, and many other popular applications and devices.