Subnet Calculator 2026
Work out the network address, broadcast address, subnet mask and usable host range for any IPv4 address and CIDR — plus a VLSM subnet splitter for dividing a network into smaller subnets.
Subnet Info or Subnet Splitter?
Use the Subnet Calculator to break down a single IP and CIDR into its network, broadcast and host range. Use the Subnet Splitter (VLSM) to divide a larger network into smaller equal-sized subnets.
IP Subnet Calculator
Enter an IPv4 address and CIDR prefix to break down the subnet
Any address inside the subnet you want to analyse — it doesn’t need to be the network address itself.
Choose the prefix length shown on your network config, e.g. /24 for 255.255.255.0.
Subnet Result
Network, broadcast, mask and usable host range
Enter an IP address and CIDR prefix, then click Calculate Subnet Details to see the full breakdown.
Subnet Splitter (VLSM)
Divide a network into equal-sized smaller subnets
The network you are starting from, before splitting it up.
How many equal-sized subnets you need to carve out of the base network.
Splitter Result
New prefix, subnet size, and the resulting subnet list
Enter your base network and split requirement, then click Split The Network to see the resulting subnets.
Common CIDR Prefixes
The most frequently used IPv4 CIDR prefixes, their equivalent dotted-decimal subnet mask, and the total vs. usable addresses each one provides.
| CIDR | Subnet Mask | Total Addresses | Usable Hosts |
|---|---|---|---|
| /8 | 255.0.0.0 | 16,777,216 | 16,777,214 |
| /16 | 255.255.0.0 | 65,536 | 65,534 |
| /20 | 255.255.240.0 | 4,096 | 4,094 |
| /24 | 255.255.255.0 | 256 | 254 |
| /26 | 255.255.255.192 | 64 | 62 |
| /28 | 255.255.255.240 | 16 | 14 |
| /30 | 255.255.255.252 | 4 | 2 |
| /31 | 255.255.255.254 | 2 | 2 (point-to-point) |
| /32 | 255.255.255.255 | 1 | 1 (host route) |
Subnet Calculator FAQ
Everything network engineers and students ask before subnetting an IPv4 network in 2026.
A subnet mask is a 32-bit value that splits an IP address into a network portion and a host portion. It is calculated from the CIDR prefix length by setting that many leading bits to 1 and the rest to 0. For example, a /24 prefix produces the subnet mask 255.255.255.0, meaning the first 24 bits identify the network and the last 8 bits identify hosts within it.
CIDR (Classless Inter-Domain Routing) notation expresses a subnet mask as a slash followed by the number of network bits, such as 192.168.1.0/24. It replaced the older class-based system (Class A, B, C) and allows networks to be sized flexibly rather than in fixed blocks.
Usable hosts are calculated as 2 raised to the number of host bits, minus 2, since the first address in the range is reserved as the network address and the last is reserved as the broadcast address. A /24 network has 8 host bits, giving 256 total addresses and 254 usable hosts. The exceptions are /31, used for point-to-point links with 2 usable addresses and no broadcast, and /32, a single host route.
The network address is the first address in a subnet, with all host bits set to 0, and identifies the subnet itself rather than a specific device. The broadcast address is the last address in the subnet, with all host bits set to 1, and is used to send data to every device on that subnet simultaneously. Neither address can be assigned to an individual host, except in /31 point-to-point links.
VLSM (Variable Length Subnet Masking) is the practice of dividing a larger network into smaller subnets of different sizes, rather than one fixed size for every subnet. It is used to allocate address space efficiently, giving a large subnet to a department that needs many hosts and a small subnet to a point-to-point link or a small office, without wasting unused addresses.
RFC 3021 defines /31 as a special case for point-to-point links, where both addresses in the two-address range are treated as usable host addresses instead of reserving one for network and one for broadcast. A /32 is a single address, effectively a host route, so it has no separate network or broadcast address at all.