Tip: click any value to copy it.
About this tool
CIDR (Classless Inter-Domain Routing) notation writes a network as an address and a prefix length after a slash — 10.0.0.0/16 means the first 16 bits are the network and the remaining bits address hosts. This calculator parses a CIDR block and expands it into the full picture: network and broadcast addresses, netmask and wildcard, the first and last usable hosts, and the total number of addresses.
It auto-detects IPv4 versus IPv6 and uses exact big-integer math, so large blocks and IPv6 ranges are accurate. Click any value to copy it. If you would rather enter the address and prefix in separate fields, use the subnet calculator — the two are cross-linked.
CIDR parsing and math happen locally — nothing leaves your browser.
Frequently asked questions
What does the number after the slash mean?
It is the prefix length — how many leading bits are fixed as the network portion. A larger number means a smaller network: /24 holds 256 addresses, /16 holds 65,536. The remaining bits address individual hosts.
How many usable hosts are in a /24?
A /24 has 256 total addresses and 254 usable hosts — the network address and the broadcast address are reserved. The calculator shows both figures for any block you enter.
Can I paste an IPv6 CIDR?
Yes — something like 2001:db8::/48 works. The tool returns the network, first and last addresses and the total address count for the range.