CIDR Calculator
Expand an IPv4 CIDR block into its network, range, mask and host count.
CIDR notation, or an address with a dotted mask (10.0.0.0 255.255.0.0).
No network entered yet
Enter an IPv4 block to see its network and broadcast addresses, usable host range, masks, host counts and scope.
Runs entirely in your browser. Your data isn't uploaded — this page makes no network request with anything you type, which you can verify in your browser's network tab. How this works.
What is the CIDR Calculator?
CIDR notation compresses a whole network into a handful of characters, which is convenient right up to the moment you need to know whether 10.20.4.0/22 overlaps the block you already allocated. Then you need the actual numbers.
Enter a block and this expands it completely: network and broadcast addresses, first and last usable host, subnet and wildcard masks, total and usable host counts, and the binary view that makes the prefix boundary obvious. You can also test whether a specific address falls inside the block, and check a list of blocks for overlaps before you commit to an address plan.
How to use it
- Enter an IPv4 block in CIDR notation, such as 10.0.0.0/16.
- Read the derived addresses, masks and host counts.
- Use the containment check to test whether a specific IP is inside the block.
- Paste additional blocks into the overlap checker to validate an address plan.
Example
Expanding a /22 block.
10.20.4.0/22
network 10.20.4.0 broadcast 10.20.7.255 usable 10.20.4.1 – 10.20.7.254 mask 255.255.252.0 wildcard 0.0.3.255 addresses 1024 (1022 usable, 1019 on AWS) scope private (RFC 1918)
Features
- Network, broadcast, first and last usable addresses
- Subnet mask, wildcard mask and prefix length, in dotted-decimal and binary
- Total and usable host counts, with the /31 and /32 special cases handled
- IP-in-block containment testing
- Overlap detection across a list of blocks
- Notes on whether the block is private, loopback, link-local or public