CIDR / Subnet Calculator
Break down a CIDR block: network address, broadcast, usable IPs, subnet mask.
About Subnet Calculator
Breaks down a CIDR block into its network address, broadcast address, subnet mask, and the range and count of usable host addresses. Subnetting math is simple in principle but easy to get wrong under time pressure, and a single off-by-one error in a subnet plan can mean an unexpected address conflict discovered only after deployment. Works for both IPv4 and IPv6 CIDR notation, since IPv6 subnetting is easy to miscalculate by hand given the much larger address space.
Why usable host count is 2 less than the address count for IPv4: the first address is reserved as the network address, the last as broadcast — a /24 has 256 total addresses but only 254 usable hosts. IPv6 doesn't reserve a broadcast address the same way, a common point of confusion moving between the two.
Common Subnets
/31 → 2 hosts (p2p)
/30 → 2 usable
/29 → 6 usable
/28 → 14 usable
/27 → 30 usable
/26 → 62 usable
/25 → 126 usable
/24 → 254 usable
/23 → 510 usable
/22 → 1022 usable
/16 → 65534 usable
/8 → 16M usable