Free CIDR / Subnet Calculator
Enter an IPv4 address and prefix length to get the network address, broadcast address, mask, and usable host range.
| Network address | |
|---|---|
| Broadcast address | |
| Subnet mask | |
| Wildcard mask | |
| Usable host range | |
| Usable hosts | |
| Total addresses |
Reading CIDR notation
The slash number in 192.168.1.0/24 counts how many bits, from the left, are "network" bits — the rest are "host" bits available to number individual devices. A /24 fixes the first 24 bits (three full octets: 11111111.11111111.11111111) and leaves the last 8 bits free, which is exactly the binary pattern that produces the familiar mask 255.255.255.0. CIDR replaced the older, rigid class A/B/C system in the early 1990s specifically so networks could be sized to the number of devices they actually needed, instead of being forced into fixed 256- or 65,536-address blocks.
Worked example: 192.168.1.0/24
With 8 host bits free, there are 2⁸ = 256 total addresses. The first (192.168.1.0) is reserved as the network address and the last (192.168.1.255) as the broadcast address, leaving 254 usable addresses for actual devices — .1 through .254. That's also why 192.168.1.0/24 is the default on so many home routers: it comes from the private address ranges reserved by RFC 1918 (10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16), and 254 devices is comfortably more than any household network needs.
Quick reference
| Prefix | Total addresses | Usable hosts |
|---|---|---|
| /30 | 4 | 2 |
| /29 | 8 | 6 |
| /28 | 16 | 14 |
| /27 | 32 | 30 |
| /24 | 256 | 254 |
Frequently Asked Questions
What do /31 and /32 mean for usable hosts?
A /32 is a single host (1 usable address, no separate network/broadcast). A /31 is a special case (RFC 3021) used for point-to-point links — both addresses in the pair are usable, with no dedicated broadcast address. Every other prefix reserves the first address for the network and the last for broadcast.
Does the IP need to be the network's first address?
No — enter any address inside the subnet and the calculator works out the correct network address for you, the same way real network tools do.
What's the difference between subnet mask and wildcard mask?
The subnet mask marks network bits with 1s and host bits with 0s (e.g., 255.255.255.0). The wildcard mask is its exact inverse (0.0.0.255) — used in contexts like Cisco access lists.
Why do routers default to 192.168.1.0/24 or 192.168.0.0/24?
Both fall inside the 192.168.0.0/16 block that RFC 1918 reserves for private networks — addresses that are never routed on the public internet. A /24 within that range gives 254 usable addresses, far more than a typical home network needs, which is why it's the near-universal factory default.
How many usable hosts does a /28 fit?
14. A /28 leaves 4 host bits (2⁴ = 16 total addresses), minus one for the network address and one for broadcast, leaving 14 assignable to devices — a common size for small office subnets.
Is my data sent anywhere?
No. All calculations happen entirely in your browser. Nothing is transmitted or stored.