If you are setting up a static IP address for a computer and need the gateway, finding the gateway address is simple, if you have a computer already setup on the network.

Below is a command which you can run on the configured computer to find the IP address of your gateway.

route -n

You should see at least one entry. If you see several, pick the entry under Gateway that is not

This number should be the IP address for your gateway.

In a home network, this is likely the same address as your router.