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CIDR & Subnet Calculator

Calculate IPv4 subnet ranges, network/broadcast addresses, usable host counts, and CIDR notation. Runs in your browser.

Runs entirely in your browser. Nothing is sent to our servers.

IPv4 address with prefix length, e.g. 192.168.1.0/24.
Enter a CIDR.
Common subnets
Common sizes

About CIDR

CIDR (Classless Inter-Domain Routing) notation expresses an IP network as an address plus a prefix length: 192.168.1.0/24 means "addresses where the first 24 bits match 192.168.1.0". The prefix tells you how many bits are network and how many are host.

What this calculator returns

  • Network address — the first address in the block (host bits all zero).
  • Broadcast address — the last address in the block (host bits all one).
  • Usable host range — the addresses you can assign to devices, excluding the network and broadcast addresses for prefixes shorter than /31.
  • Subnet mask — the dotted decimal mask equivalent, e.g. 255.255.255.0 for /24.
  • Wildcard mask — the inverse of the subnet mask, used by Cisco ACLs.
  • Total / usable count — how big the block is.

/31 and /32 are special

Traditionally the network address and broadcast address are reserved, leaving 2^h − 2 usable hosts. But RFC 3021 lets /31 networks use both addresses as point-to-point endpoints, giving 2 usable hosts. And /32 is a single address — useful for host routes and loopbacks.

Frequently asked questions

Does this handle IPv6?
Not in this version — it's IPv4 only. IPv6 subnet math is similar in concept but with 128-bit addresses; a v6 calculator is on the planned list.
Why does /24 give 254 usable hosts instead of 256?
A /24 block contains 256 addresses, but two of them are reserved: the network address (all host bits 0) and the broadcast address (all host bits 1). Most hosts can't use those.
What's the difference between a subnet mask and a wildcard mask?
They're inverses. 255.255.255.0 is the subnet mask for /24; 0.0.0.255 is the corresponding wildcard mask. Cisco ACLs use wildcard masks; almost everything else uses subnet masks.
Can I paste a non-network address (like a host) and get the network it belongs to?
Yes — the calculator masks off the host bits automatically. Paste 192.168.1.42/24 and you'll see the same network as 192.168.1.0/24.

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Last updated: May 17, 2026