How to Calculate Hosts Per Subnet

A subnet mask is a TCP/IP networking setting that blocks off specific IP addresses from the rest of the network. Without the use of the subnet mask, all 4,294,967,296 possible IP addresses would need to be considered by the router for every networking connection, which would slow down Internet transactions considerably. The subnet mask uniquely identifies how many hosts are available per subnet.

Instructions

1. Convert the IP address for the subnet mask you wish to calculate into binary notation. For example, if the subnet mask is 255.255.255.0, that would convert into 11111111.11111111.11111111.00000000.

2. Perform a logical NOT operation on the binary subnet mask. For example, the NOT operation on the previous subnet mask is: 00000000.00000000.00000000.11111111.

3. Convert the binary number back into decimal, then add 1. For the example we are using, this number is 256. You must add one in order to include the full range from 0 to 255, or 256 total addresses. One of these addresses will always be assigned to the router handling that subnet.