Skip to content
English
All tools

Categories

Developer ToolsEncoding & DecodingJSON & DataHash & ChecksumText ToolsDate & TimeNetwork ToolsFile ToolsMarkdown & Diagrams

Subnet Calculator

Divide a network such as 192.168.0.0/24 into 4 subnets, or into /26 blocks, and get a ready-to-use allocation table.

Processed locally in your browser

Options

Used in "Number of subnets" mode; rounded up to a power of two.

Used in "New prefix length" mode (e.g. 26 for /26 subnets).

0 chars · 0 lines
The result will appear here.

What is Subnet Calculator?

Subnetting borrows bits from the host part of an address to create several smaller networks. Splitting a /24 into four subnets borrows two bits and gives four /26 networks of 64 addresses each (62 usable hosts).

Enter the parent network, then choose either the number of subnets you need or the prefix length you want. The tool lists every subnet with its network address, first and last host, broadcast address and usable hosts, up to 1,024 rows, and also gives a plain list of CIDR blocks to copy.

How does it work?

  1. Type the parent network in CIDR form, for example 192.168.0.0/24 or 2001:db8::/48.
  2. Pick "Number of subnets" (rounded up to a power of two) or "New prefix length".
  3. Review the subnet table; the note under it shows how many subnets exist in total.
  4. Copy the list of CIDR blocks into your addressing plan or firewall configuration.

Common use cases

  • Carving a /24 site network into one subnet per department or VLAN.
  • Planning an IPv6 allocation by splitting a /48 into /64 LAN prefixes.
  • Preparing VLSM: allocate the biggest subnet first, then split the leftover block again.
  • Documenting an addressing plan with exact first/last hosts for each subnet.

Examples

Try this input in the tool above:

Input
192.168.0.0/24
Output
192.168.0.0/26
192.168.0.64/26
192.168.0.128/26
192.168.0.192/26

Privacy

Subnet Calculator runs entirely in your browser. The text or files you provide are processed on your device and are not uploaded, logged or stored on our servers.

Limitations

Only equal-size splits are produced in one pass. For unequal sizes (VLSM) split repeatedly. The table is capped at 1,024 rows; the total count is still reported exactly.

Frequently asked questions

Why did I get 8 subnets when I asked for 5?

Equal subnets always come in powers of two because each extra bit doubles the count. The tool rounds 5 up to 8 and tells you so.

How does this relate to VLSM?

VLSM (variable-length subnet masks) uses different prefix lengths in one network. Split once for the biggest need, keep one block, and split that block again for smaller needs.

Is the first subnet ever unusable?

Not with modern equipment: the "subnet zero" and the all-ones subnet are valid in classless networks. Only the host-level network and broadcast addresses are reserved.

Related tools

More tools in Network Tools →