@mlsbraves: the default gateway might be outside of this address range.
It is perfectly legal to have a link with say: 192.168.1.2/24 (where default gw is 192.168.1.1)
And this network range is routed to 192.168.1.2...
192.168.1.2/24 (where default gw is 192.168.1.1)
If your getting this information from your ISP you will also want to confirm with them what the gateway IP is. You will need this to configure your equipment and the gateway IP will not be available to use.
Typically if an ISP has given me something like x.x.54.128 /27 than x.x.54.129 is configured as the gateway. In that case your usable would be .130-158. Most ISP use the first available for the gateway but I know Comcast uses the last for some reason.