CIDR subnet
readyType a CIDR block - get network, broadcast, host range, mask, wildcard, total + usable hosts, and the binary breakdown. Works for IPv4 and IPv6.
Binary (network bits highlighted)
[01] Quick reference
| CIDR | Mask | Hosts | Common use |
|---|---|---|---|
/8 | 255.0.0.0 | 16,777,214 | RFC1918 10.0.0.0/8 private |
/12 | 255.240.0.0 | 1,048,574 | RFC1918 172.16.0.0/12 |
/16 | 255.255.0.0 | 65,534 | Class B / RFC1918 192.168.0.0/16 |
/24 | 255.255.255.0 | 254 | Typical LAN subnet |
/29 | 255.255.255.248 | 6 | Small point-to-point |
/30 | 255.255.255.252 | 2 | Router-to-router link |
/31 | 255.255.255.254 | 2 (RFC 3021) | P2P, no broadcast |
/32 | 255.255.255.255 | 1 | Single host route |
[02] How CIDR works
CIDR ("Classless Inter-Domain Routing") replaced the old A/B/C class system in 1993. Instead of fixed boundaries, the prefix length (the /N) tells you how many bits identify the network. Everything beyond those bits identifies the host.
For 192.168.1.0/24: the first 24 bits (192.168.1) are the network. The last 8 bits are host. That gives 28 = 256 addresses, of which 254 are usable hosts (network address and broadcast are reserved).
[03] IPv6 differences
IPv6 uses 128-bit addresses, written in 8 groups of 4 hex digits. Common prefixes: /48 (site), /56 (smaller site), /64 (single LAN - the default for SLAAC). There's no broadcast address and the network/host distinction works the same way at the bit level.
Common questions
Is CIDR / Subnet Calculator free to use?
Yes. The tool runs in your browser at no cost, with no signup required.
Where is the math performed?
Calculations run locally in your browser. Your inputs do not leave your device.
Are the rates and rules current?
We update sources when published rates change. For high-stakes decisions, verify against the official source linked on this page.