How to Check COM Ports in Windows 10

To check COM ports in Windows 10, right-click Start, select Device Manager, and expand Ports (COM & LPT). Each serial device is listed with its port number in brackets, such as (COM3).

Applies to: Windows 10. Checked against Microsoft Learn on September 27, 2026.

Check COM ports in Device Manager

1. Right-click Start and select Device Manager. See how to open Device Manager in Windows 10.
2. Select the arrow next to Ports (COM & LPT).
3. The COM number is at the end of each device’s name.

Don’t see Ports (COM & LPT)? Plug the device in, then select Action > Scan for hardware changes. If it’s still missing, the device may need a driver from its maker. To see ports for devices that aren’t plugged in, select View > Show hidden devices.

Check with a command

In Command Prompt, run mode. It lists each COM port and its settings.

In PowerShell, run:

[System.IO.Ports.SerialPort]::GetPortNames()

It lists the COM port names, such as COM3 and COM4.

Change a COM port number

Some older apps only work with low numbers, like 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 in COM Port Number and select OK.

If Windows says the number is in use, it may belong to a device that isn’t plugged in. Pick a different number unless you’re sure that device is gone.

Work out which port belongs to your device

If several COM ports are listed, keep Device Manager open on Ports (COM & LPT), unplug your device, and watch which entry disappears. Plug it back in and the same port returns. You can also double-click a port, open the Details tab, and choose Bus reported device description to see the name the device reports, such as the name of an Arduino board or a USB-to-serial adapter.

If the COM port is missing or won’t open

• The device shows under Other devices with a warning. Windows has no driver for its USB-to-serial chip. Common chips are FTDI, CH340, Silicon Labs CP210x, and Prolific. Download the driver from the chip maker or the device maker.
• A Prolific adapter shows “PL2303HXA PHASED OUT” or Code 10. Newer Prolific drivers don’t support older or counterfeit chips. Use an adapter with a supported chip instead.
• Your app says “Access denied” or “port in use.” Only one app can use a COM port at a time. Close other serial programs, such as a terminal app or the Arduino IDE’s Serial Monitor.
• The port number keeps changing. Windows assigns a new number when you use a different USB port. Plug the device into the same USB port each time, or set a fixed number as shown above.
• Many old numbers say “(in use).” Those are reserved for devices you’ve connected before. Turn on View > Show hidden devices and uninstall faded ports you no longer need.

Frequently asked questions

Is a COM port the same as a USB port?

No. A USB-to-serial adapter or device shows up as a COM port, but the USB port itself doesn’t. To see what’s plugged into USB, see how to see connected USB devices in Windows 10.

Is a COM port the same as a network port?

No. Network ports are numbers apps use to talk over a network. See how to find port numbers in Windows 10.

How do I do this in Windows 11?

See how to check COM ports in Windows 11.

What baud rate should I use?

Use whatever the device’s manual says, often 9600 or 115200. The speed in Device Manager’s Port Settings is only a default. Most programs set their own speed when they open the port, and both ends must match or you’ll see garbled text.

My PC has no serial port. What do I need?

A USB-to-serial adapter. Once its driver is installed, it shows up as a COM port in Device Manager like a built-in one.

Microsoft’s reference is mode. More help is on our Windows Help & Guides page.