|Total-addresses: how many unique addresses can be represented. To determine how many are available to be assigned to devices you need to subtract 2 from the provided number to allow for the ‘network’ and ‘broadcast’ address. A further one of these may need to be assigned to a router.
eg: 192.168.1.0/25 would include all address between 192.168.1.0 and 192.168.1.127.
eg: 192.168.1.128/25 would include all address between 192.168.1.128 and 192.168.1.255