IP Subnet Calculator 2026 — IPv4 & VLSM
Work out network address, broadcast address, usable host range, and wildcard mask from any IPv4 address and CIDR or subnet mask — plus a subnet-splitter for dividing a network into smaller VLSM subnets.
Subnet Info or Subnet Splitter?
Use the subnet calculator to analyse a single IP address and mask — network address, broadcast, usable range, and more. Use the splitter when you need to divide one network into several smaller subnets for VLSM planning.
IPv4 Subnet Calculator
Enter an IP address and CIDR/mask to see the full subnet breakdown
Any IPv4 address in dotted-decimal notation.
Choose the subnet mask as a CIDR prefix. /24 is the most common LAN size.
Subnet Result
Network, broadcast, usable range, and wildcard mask
Enter an IPv4 address and CIDR, then click Calculate Subnet Details to see the full breakdown.
Subnet Splitter (VLSM)
Divide a network into equally sized smaller subnets
The starting network address you want to divide up.
Rounded up to the nearest power of 2 — e.g. asking for 5 subnets creates 8.
Splitter Result
New prefix length, subnet size, and first few subnets
Enter a base network and how many subnets you need, then click Split This Network to see the result.
CIDR Quick Reference
The most commonly used CIDR prefixes and how many usable hosts each one provides.
| CIDR | Subnet Mask | Usable Hosts |
|---|---|---|
| /24 | 255.255.255.0 | 254 |
| /25 | 255.255.255.128 | 126 |
| /26 | 255.255.255.192 | 62 |
| /27 | 255.255.255.224 | 30 |
| /28 | 255.255.255.240 | 14 |
| /29 | 255.255.255.248 | 6 |
| /30 | 255.255.255.252 | 2 |
| /31 | 255.255.255.254 | 2 (point-to-point) |
| /32 | 255.255.255.255 | 1 (single host) |
IP Subnet Calculator FAQ
Everything network admins and students ask before subnetting in 2026.
A subnet mask is a 32-bit value that splits an IPv4 address into a network portion and a host portion, telling devices which addresses belong to the same local network. It’s usually written in dotted-decimal form like 255.255.255.0, or as a CIDR prefix like /24, both of which represent the same 24 leading “network” bits.
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 addressing system and lets network size be defined flexibly rather than only in fixed Class A, B, or C blocks.
For a subnet with n host bits, the total number of addresses is 2 to the power of n. Two of those addresses are reserved — the network address and the broadcast address — so the number of usable host addresses is 2^n minus 2. The exceptions are a /31, which has exactly 2 usable addresses under point-to-point link rules, and a /32, which represents a single host address.
A wildcard mask is the bitwise inverse of a subnet mask, most commonly used in access control lists (ACLs) on routers and firewalls. Where a subnet mask uses a 1 bit to mean “must match” and 0 to mean “don’t care” for the host portion, a wildcard mask flips this so 0 means “must match” and 1 means “don’t care”.
VLSM (Variable Length Subnet Masking) is the practice of subdividing a network into subnets of different sizes rather than one fixed size, so each subnet only gets as many addresses as it actually needs. This reduces wasted IP address space compared to splitting a network into equally sized subnets regardless of how many hosts each one requires.
Private IP ranges — 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16 — are reserved for use inside local networks and are not routed on the public internet, so the same private addresses can be reused by many different networks. Public IP addresses are globally unique and routable, and are assigned by regional internet registries to ISPs and organisations.