Subnet Splitter (VLSM)
Split one IP block into multiple smaller subnets and list each range and host count.
The subnet splitter divides one IPv4 CIDR block (e.g. 192.168.0.0/24) into smaller, equal-sized subnets and shows each child subnet's network address, first/last usable host, broadcast address and usable host count at a glance. Before you start a VLSM (Variable Length Subnet Mask) design, it answers "if I split a /24 into /26s, how many do I get and where does each range end?" in one step.
Enter a base CIDR and a new prefix length (a number larger than the base prefix). The number of child subnets is 2(new prefix − base prefix). To inspect the host range of a single block, use the CIDR calculator; to fold a start/end IP pair back into CIDR, use the IP range to CIDR converter.
| Base network | 192.168.0.0/24 |
|---|---|
| New prefix | /26 |
| Child subnets | 4 |
| Usable hosts per subnet | 62 |
| Network | First host | Last host | Broadcast | Hosts |
|---|---|---|---|---|
| 192.168.0.0/26 | 192.168.0.1 | 192.168.0.62 | 192.168.0.63 | 62 |
| 192.168.0.64/26 | 192.168.0.65 | 192.168.0.126 | 192.168.0.127 | 62 |
| 192.168.0.128/26 | 192.168.0.129 | 192.168.0.190 | 192.168.0.191 | 62 |
| 192.168.0.192/26 | 192.168.0.193 | 192.168.0.254 | 192.168.0.255 | 62 |
How subnet splitting works
When you choose a new prefix longer than the base, the number of subnets grows as a power of two for each added bit. Splitting a /24 into /26 yields 2(26−24) = 4 subnets, and each holds 2(32−26) = 64 addresses (62 usable hosts).
- Network address: the first address of the subnet (not usable as a host).
- First usable host: network address + 1.
- Last usable host: broadcast − 1.
- Broadcast: the last address of the subnet.
- Usable hosts: 2(32−prefix) − 2.
The /31 and /32 special cases
The usual formula subtracts two addresses (network and broadcast), but a /31 used for point-to-point links treats both addresses as usable per RFC 3021, giving 2 usable hosts. A /32 is a single host (loopback, load-balancer VIP, etc.) and is shown as 1. This tool applies these exceptions automatically.
Even if the base network is given on an unaligned address (e.g. 192.168.0.5/24), the tool first normalizes it to the true network address (192.168.0.0) before splitting, so results always land on clean boundaries.
Quick reference: splitting a /24 into smaller prefixes
Here is the most common case — carving a single /24 into smaller prefixes — laid out in a table. Each extra bit in the new prefix doubles the number of subnets and roughly halves the usable hosts per subnet. The usable host count is 2(32−prefix) − 2.
| New prefix | Subnets | Usable hosts each | Total addresses each |
|---|---|---|---|
/25 | 2 | 126 | 128 |
/26 | 4 | 62 | 64 |
/27 | 8 | 30 | 32 |
/28 | 16 | 14 | 16 |
/29 | 32 | 6 | 8 |
/30 | 64 | 2 | 4 |
Worked example: splitting 192.168.1.0/24 into /26
Take the base block 192.168.1.0/24 (256 addresses) and split it into /26. That yields 2(26−24) = 4 subnets, each holding 64 addresses (62 usable hosts). Notice how the last octet steps by 64: 0 → 64 → 128 → 192.
| Subnet | Network address | Usable range | Broadcast |
|---|---|---|---|
192.168.1.0/26 | 192.168.1.0 | 192.168.1.1 – 192.168.1.62 | 192.168.1.63 |
192.168.1.64/26 | 192.168.1.64 | 192.168.1.65 – 192.168.1.126 | 192.168.1.127 |
192.168.1.128/26 | 192.168.1.128 | 192.168.1.129 – 192.168.1.190 | 192.168.1.191 |
192.168.1.192/26 | 192.168.1.192 | 192.168.1.193 – 192.168.1.254 | 192.168.1.255 |
Together the four subnets cover the original 256 addresses (0–255) with no gaps: the address right after the first subnet's broadcast (.63) is the network address of the second subnet (.64), and so on. Every block shares the mask 255.255.255.192. To cross-check a single block's mask and wildcard, run it through the CIDR calculator.