How to Calculate Subnet Range

Calculate the subnet mask range for your network.

Large networks use subnets as a way to segment the client machines connected to the routers. A subnet helps contain a group of computers on one part of your network while still allowing for more computers in another area of your network. When you create a subnet mask, the numbers used identify how many subnets you can have on your network. Perform this calculation by converting the subnet mask numbers to binary and doing some simple multiplication.

Instructions

1. Convert your subnet mask to binary. In this example, the subnet mask 255.255.224.0 is used. The last octet is used to determine the subnet range. It's this last octet (224) that you convert to binary. You convert a number by placing a 1 underneath each binary number until it adds up to the decimal number 224. The following lays out a binary number conversion:

   254---128---64---32---16---8---4---2---1

   0--------1------1-----1-----0---0---0---0----0

   The conversion of 224 is "01110000." This number is used to determine your subnet range.

2. View the number of "1" bits. The "1" bit is used in the calculation to determine your subnet range. In the number conversion in step one, there are a total number of 3 "1" bits.

3. Calculate the total subnet range. Since subnets are calculated using base two, the number of "1" bits is the exponent for two. This total calculation tells you how many subnets are available. The following calculation determines this range for the subnet octet 254:

   2^3 = 8 subnets

   The "^" character in this calculation means "2 raised to the power of 3."

References

• Josh Gentry: Classful IP Subnet Calculations