How do I find my subnet mask on my computer?

START > RUN > Type CMD > type IPCONFIG /ALL

There is a space between the g and forward slash. You will have to scroll to the adapter connected to the network and it will show you your IP Address, Subnet, Default Gateway, DNS Servers, DHCP enabled/disabled etc...

-Click on start
-click on run or search & type "cmd" in the box
-Enter the text "ipconfig /all" in the black window that opens on your desktop.
-Scroll through the data that appears on the window. There may be numerous entries depending on what adapters your system has installed. Look for the text "Subnet Mask" and "Default Gateway." The text will be located to the right of its label in the form of an IP address, such as 255.255.255.0