Expand a CIDR block into its network address, broadcast address, subnet mask, and usable host range.
Enter an IPv4 address and prefix length in CIDR notation (e.g., 10.0.0.0/16).
Click "Calculate" to expand the block.
Review the network address, broadcast address, mask, and usable host range.
Network address, broadcast address, subnet mask, wildcard mask, total address count, usable host range, and usable host count for any IPv4 CIDR block from /0 to /32.
Misreading a CIDR block is a common source of firewall and allowlist mistakes -- allowing too few addresses blocks legitimate traffic, and allowing too many opens up unintended ranges. Getting the math right before you configure infrastructure prevents both failure modes.
The calculator converts the IPv4 address to a 32-bit integer, builds the subnet mask by left-shifting from the prefix length, and derives the network address (AND with the mask) and broadcast address (OR with the inverted mask). Usable hosts exclude the network and broadcast addresses for prefixes shorter than /31. Everything runs as plain arithmetic in your browser -- no address is sent anywhere.
The number after the slash is the prefix length -- how many leading bits of the 32-bit address are fixed as the network portion. A /24 fixes the first 24 bits, leaving 8 bits (256 addresses, 254 usable) for hosts. A smaller number means a larger block: /16 covers 65,536 addresses.
The first address in a block identifies the network itself, and the last is reserved as the broadcast address for that segment. Both are excluded from the usable host range for any prefix shorter than /31, which is why a /24 has 256 total addresses but only 254 usable hosts.
No, this calculator handles IPv4 CIDR notation only. IPv6 subnetting uses 128-bit addresses and different conventions (no broadcast address, for example), and is out of scope for this tool.
Run this check again from a clean all proxy types exit and see what actually reaches the other side.