Subnet and PortsSubnet splitter: divide a network into equal subnets
Pick a network and a longer prefix. The tool lists every subnet you get, with its usable range.
What it does
You give a network (192.168.10.0/24) and a new prefix (/26). The network is cut into equal blocks of that size: a /24 contains four /26 blocks of 64 addresses each, with 62 usable hosts. The table lists each block's address, first and last host, and broadcast address. Only the first 256 blocks are listed when there are more.
How many subnets and how big
Each extra prefix bit doubles the number of subnets and halves the size of each:
| New prefix inside a /24 | Subnets | Addresses each | Usable hosts each |
|---|---|---|---|
| /25 | 2 | 128 | 126 |
| /26 | 4 | 64 | 62 |
| /27 | 8 | 32 | 30 |
| /28 | 16 | 16 | 14 |
| /29 | 32 | 8 | 6 |
| /30 | 64 | 4 | 2 |
Choosing the size
- Count the devices that each subnet must hold now, then allow room for growth (a common rule of thumb is to leave 25 to 50 percent free).
- Add 2 for the network and broadcast addresses.
- Pick the smallest block with enough addresses.
- If your subnets differ in size (a big office LAN and several small links), this tool gives equal blocks only. Plan the big one first, then split what remains: that is called variable-length subnet masking.
Example: an office with four departments
You have 192.168.10.0/24 and four departments of at most 50 devices each. A /26 gives 62 hosts per department with room to grow. The tool shows the four subnets: 192.168.10.0/26, 192.168.10.64/26, 192.168.10.128/26 and 192.168.10.192/26.
Common mistakes
- Choosing a prefix shorter than the network. You cannot split a /24 into /23s; the new prefix must be longer.
- Using the broadcast address of one subnet as a host in the next. Each subnet has its own first and last usable address.
- Forgetting routing. Each subnet needs a router interface or a VLAN in the real network.
We checked the split lists against Python's ipaddress module on 100 random networks.
Can I split into subnets of different sizes?
Not with this tool. Allocate the largest subnet first and divide what is left.
Which prefix gives 30 hosts?
A /27: 32 addresses, 30 usable.
This is an independent guide. It is not connected with IANA, the IETF or any network equipment maker. Address and port data come from the IANA registries as fetched on 14 November 2026; RFC texts were read from rfc-editor.org. Check the originals for anything you rely on.