Common prefix sizes
| CIDR | Netmask | Addresses | Usable hosts |
|---|---|---|---|
| /8 | 255.0.0.0 | 16,777,216 | 16,777,214 |
| /16 | 255.255.0.0 | 65,536 | 65,534 |
| /22 | 255.255.252.0 | 1,024 | 1,022 |
| /24 | 255.255.255.0 | 256 | 254 |
| /26 | 255.255.255.192 | 64 | 62 |
| /28 | 255.255.255.240 | 16 | 14 |
| /30 | 255.255.255.252 | 4 | 2 |
| /31 | 255.255.255.254 | 2 | 2 (RFC 3021) |
| /32 | 255.255.255.255 | 1 | 1 (single host) |
Related tools
Identify who operates a network with the IP lookup (geolocation, ASN, VPN and Tor detection), browse ASN pages, or check which ports are open on your own IP.
Frequently Asked Questions
What does CIDR notation like /24 mean?
The number after the slash is how many bits of the address identify the network. A /24 fixes the first 24 bits, leaving 8 bits for hosts: 256 addresses, of which 254 are usable (network and broadcast addresses are reserved).
How many usable hosts does a subnet have?
2^(32 minus prefix) minus 2, because the first address names the network and the last is the broadcast. Exceptions: a /31 has 2 usable addresses (point-to-point links, RFC 3021) and a /32 is a single host.
Is anything sent to a server?
No. The calculation runs entirely in your browser with JavaScript; the addresses you type are never transmitted or stored.