CIDR Calculator — Network, Broadcast & Host Range
Enter any IPv4 CIDR (e.g. 10.0.0.0/24) and get the network address, broadcast, first/last usable hosts, host count, subnet mask and wildcard mask instantly.
Last reviewed 2026-10-19. Rates change — verify against the official sources linked below before relying on these figures.
What this is based on
- IPv4 only — IPv6 subnetting uses 128-bit math and different conventions.
- /31 links (RFC 3021 point-to-point) report both addresses as usable; /32 is a single host.
- Host count for prefixes ≤ /30 excludes the network and broadcast addresses.
- Everything runs locally in your browser — pasted content is never uploaded, logged or stored.
Reading a CIDR in seconds
The /number is how many bits are fixed as the network part. /24 pins the first three octets — 256 addresses, 254 usable. Every +1 on the prefix halves the space: /25 gives two subnets of 126 hosts, /26 gives four of 62.
The practical math: hosts ≈ 2^(32−prefix) − 2. A /22 is 1024 addresses — the size you actually need for a ~1000-device LAN, which is why 'just use /24 everywhere' runs out.
The two edge prefixes
/31 has exactly two addresses and no broadcast — defined by RFC 3021 for point-to-point links between routers, where wasting a /30 (4 addresses for 2 endpoints) is silly.
/32 is a single host — it's how firewall rules and route advertisements name one machine exactly.
Frequently asked questions
- How many hosts are in a /24?
- 256 addresses, 254 usable — the network (x.x.x.0) and broadcast (x.x.x.255) addresses are reserved.
- What is a wildcard mask?
- The bitwise inverse of the subnet mask (0.0.0.255 for /24) — used in Cisco ACLs and OSPF where 'wildcard' means 'bits to ignore'.
- Is 10.0.0.0/8 a valid network?
- Yes — the entire private 10.x space. The address ending in .0 is valid as a network address, it's just not assignable to a host.
- Why does my provider give me a /29?
- That's 8 addresses, 6 usable — enough for a router plus a handful of public-facing servers, which is exactly what a small static-IP package is.
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