Enter an IP or CIDR block and see the full breakdown, bit by bit.
Paste a full CIDR like 10.20.0.0/22 into the IP field — the prefix is picked up automatically.
A wildcard mask is the bitwise inverse of the subnet mask: network bits become 0 and host bits become 1. For a /24 (subnet mask 255.255.255.0) the wildcard mask is 0.0.0.255. Wildcard masks are used in Cisco ACLs and OSPF network statements.
Count the 1 bits in the subnet mask: that count is the prefix length. 255.255.255.0 has 24 one-bits, so it is /24; 255.255.240.0 has 20, so it is /20. The bit grid above colors those network bits, so you can count them.
A /24 contains 256 addresses. In a standard subnet 254 are usable, because the network and broadcast addresses are excluded. In the cloud, AWS and Azure reserve 5 addresses per subnet (251 usable) and Google Cloud reserves 4 (252 usable).
A /32 is a single IP address, commonly used for host routes, loopbacks and firewall rules. A /31 has two addresses and, per RFC 3021, both are usable on point-to-point links because no network or broadcast address is needed.
AWS reserves 5 (network, VPC router .1, DNS .2, future use .3, broadcast), Azure reserves 5 (network, gateway .1, Azure DNS .2 and .3, broadcast) and Google Cloud reserves 4 (network, gateway .1, second-to-last address, broadcast). Select a provider above to see the exact reserved addresses for your block.