IPv4 Subnet Calculator
Split an IPv4 network into equal subnets and list the CIDR block, address range, first and last host, and usable host count of each piece you get.
How to use
- Enter the parent block in CIDR notation.
- Set how many subnets you need.
- Read the CIDR, range, and host count of each piece.
Subnetting divides a network into smaller blocks, most often so one network does not span a large broadcast domain. This calculator splits a parent block into the smallest equal set that gives at least the number of subnets you asked for.
Enter a parent network above.
Subnets
| CIDR | Range | First host | Last host | Usable hosts |
|---|---|---|---|---|
Questions about ipv4 subnet calculator
- Why do I get more subnets than I asked for?
- Subnet sizes are powers of two, so the count is rounded up to the next power of two. Asking for five gives eight.
- How do I borrow the extra bits?
- Each extra prefix bit halves the block and doubles the number of subnets, which is why the prefix grows by the ceiling of the binary logarithm.
- What if the parent is too small?
- The calculator says so rather than producing an invalid block.
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