Subnet Calculator

Calculate How Many Subnets you need

What is a Subnet

Subnetting is when the network is broken into different block sections using logical addresses to segregate each block. Internet Protocol (IP) has two parts a network address and a host address. Subnet mask is used to determine how many bits will be used to represent the network address. Subnetting is great to split up the network into more manageable sections or different departments. Subnet masks are 32 bits in length the network bits are in all “1” s and the host bits are in “0” s. In each subnet two addresses are reserved for the network address which ends in 0 and the broadcast address which ends in 1. These reserved addresses cannot be used for the hosts on each subnet the rest of the addresses in the subnet can be used. This enables network administrators to better utilize the available address and helps have more realistic host limits that is not restrained to A, B and C class limits.

CIDR Conversion Table

CIDR HostsNetmask BinarySubnet Mask
/24 254 11111111 11111111 11111111 00000000255.255.255.0
/25 128 11111111 11111111 11111111 10000000255.255.255.128
/26 64 11111111 11111111 11111111 11000000255.255.255.192
/27 32 11111111 11111111 11111111 11100000255.255.255.224
/28 16 11111111 11111111 11111111 11110000255.255.255.240
/29 8 11111111 11111111 11111111 11111000255.255.255.248
/30 4 11111111 11111111 11111111 11111100255.255.255.252


Can be created using any of the IP classes A, B and C but these can have limitation due to the fixed network ID length such as 8, 16 and 24. Subnet gives the ability to have the network ID of any length of our choosing. Subnet mask is used to determine how long the network ID length is and how many bits is allocated to the network ID and host ID and tells the router which part of the address network ID and host ID.


CIDR stands for (Classes Inter-Domain Routing) is used to represent an IP address range and the network mask for example “” where the x’s represent the IP address of the CIDR and “n” being the network prefix.

Subnet Table

CIDRSubnet MaskTotal Addresses Usable Addresses

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