Subnet Calculator with VLSM

Understanding IP Subnetting

Subnetting is a method of dividing a larger IP network into smaller, more manageable sub-networks (subnets). Each subnet has its own network address, broadcast address, and usable host range.

In IPv4, a subnet is defined by its CIDR notation — for example, 192.168.1.0/24 indicates the first 24 bits are reserved for the network, and the remaining bits define host addresses.

The number after the slash (/) is the prefix length, and it determines how many IP addresses are in the subnet. The smaller the prefix, the more host addresses available. For example:

/24 = 256 total IPs, 254 usable hosts
/26 = 64 total IPs, 62 usable hosts
/30 = 4 total IPs, 2 usable (often used for point-to-point links)

This tool also demonstrates Variable Length Subnet Masking (VLSM), where larger networks are subdivided into smaller blocks based on specific size needs.

Enter any CIDR block below to get key subnetting information and a breakdown of all usable IP ranges.

Enter a CIDR to calculate subnet details.

IPv4 Reference Chart (/8 → /30)

/8 → 16,777,216 addresses (16,777,214 usable) — 65,536 /24 networks
/9 → 8,388,608 addresses (8,388,606 usable) — 32,768 /24 networks
/10 → 4,194,304 addresses (4,194,302 usable) — 16,384 /24 networks
/11 → 2,097,152 addresses (2,097,150 usable) — 8,192 /24 networks
/12 → 1,048,576 addresses (1,048,574 usable) — 4,096 /24 networks
/13 → 524,288 addresses (524,286 usable) — 2,048 /24 networks
/14 → 262,144 addresses (262,142 usable) — 1,024 /24 networks
/15 → 131,072 addresses (131,070 usable) — 512 /24 networks
/16 → 65,536 addresses (65,534 usable) — 256 /24 networks
/17 → 32,768 addresses (32,766 usable) — 128 /24 networks
/18 → 16,384 addresses (16,382 usable) — 64 /24 networks
/19 → 8,192 addresses (8,190 usable) — 32 /24 networks
/20 → 4,096 addresses (4,094 usable) — 16 /24 networks
/21 → 2,048 addresses (2,046 usable) — 8 /24 networks
/22 → 1,024 addresses (1,022 usable) — 4 /24 networks
/23 → 512 addresses (510 usable) — 2 /24 networks
/24 → 256 addresses (254 usable) — 1 /24 network
/25 → 128 addresses (126 usable)
/26 → 64 addresses (62 usable)
/27 → 32 addresses (30 usable)
/28 → 16 addresses (14 usable)
/29 → 8 addresses (6 usable)
/30 → 4 addresses (2 usable)