How to use
- Enter an IP address with a prefix (/24) or a netmask (/255.255.255.0). Without a prefix, a single address is assumed.
- Read the network address, masks, usable host range and number of hosts.
- Enter a longer prefix under Split into subnets to divide the network.
- Type an address under Check to see whether it is inside the range.
Options explained
- Usable hosts
- In IPv4 the first address is the network and the last is the broadcast, so a /24 has 254 usable hosts. /31 point-to-point links (RFC 3021) and /32 single addresses use every address. IPv6 has no broadcast address.
- Wildcard mask
- The inverse of the subnet mask, used in Cisco ACLs and OSPF — 0.0.0.255 for a /24.
- Address type
- Flags private (RFC 1918), carrier-grade NAT, loopback, link-local, multicast and documentation ranges.
Prefix cheat sheet
| Prefix | Netmask | Addresses | Usable hosts |
|---|---|---|---|
| /30 | 255.255.255.252 | 4 | 2 |
| /29 | 255.255.255.248 | 8 | 6 |
| /28 | 255.255.255.240 | 16 | 14 |
| /27 | 255.255.255.224 | 32 | 30 |
| /26 | 255.255.255.192 | 64 | 62 |
| /25 | 255.255.255.128 | 128 | 126 |
| /24 | 255.255.255.0 | 256 | 254 |
| /23 | 255.255.254.0 | 512 | 510 |
| /22 | 255.255.252.0 | 1,024 | 1,022 |
| /16 | 255.255.0.0 | 65,536 | 65,534 |
IPv4 CIDR cheat sheet
| Prefix | Subnet mask | Addresses | Usable hosts |
|---|---|---|---|
| /8 | 255.0.0.0 | 16,777,216 | 16,777,214 |
| /12 | 255.240.0.0 | 1,048,576 | 1,048,574 |
| /16 | 255.255.0.0 | 65,536 | 65,534 |
| /20 | 255.255.240.0 | 4,096 | 4,094 |
| /22 | 255.255.252.0 | 1,024 | 1,022 |
| /23 | 255.255.254.0 | 512 | 510 |
| /24 | 255.255.255.0 | 256 | 254 |
| /25 | 255.255.255.128 | 128 | 126 |
| /26 | 255.255.255.192 | 64 | 62 |
| /27 | 255.255.255.224 | 32 | 30 |
| /28 | 255.255.255.240 | 16 | 14 |
| /29 | 255.255.255.248 | 8 | 6 |
| /30 | 255.255.255.252 | 4 | 2 |
| /31 | 255.255.255.254 | 2 | 2 (point-to-point links, RFC 3021) |
| /32 | 255.255.255.255 | 1 | 1 (a single host) |
Usable hosts are the addresses minus the network and broadcast addresses, except for /31 and /32 where nothing is reserved.
Example
192.168.1.130/26 belongs to the network 192.168.1.128/26: usable hosts run from 192.168.1.129 to 192.168.1.190, and 192.168.1.191 is the broadcast address — 62 hosts in total.
The private ranges from RFC 1918 are 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16; home routers usually hand out addresses from a /24 inside 192.168.0.0/16.
Frequently asked questions
How many hosts are in a /24, /16 or /8?
254, 65,534 and 16,777,214 usable hosts. The total address count is 2 to the power of (32 − prefix).
How do I split a /24 into four subnets?
Use a /26. Each /26 has 64 addresses (62 usable) — .0, .64, .128 and .192.
Does it support IPv6?
Yes. Addresses are shown in the standard compressed form (RFC 5952) and fully expanded, and prefixes up to /128 are supported.
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