IP Subnet Calculator
Calculate network address, broadcast, mask and usable host range from CIDR.
What the IP Subnet Calculator does
A CIDR prefix says how many leading bits identify the network. Everything after those bits addresses hosts inside it, so the prefix length alone determines the subnet mask, the block size and how many hosts the subnet can hold.
Formula
Subnet mask = 32 bits with the first /n setNetwork = IP AND MaskBroadcast = Network OR WildcardUsable hosts = 2^(32 − n) − 2
Inputs explained
| Input | Unit | Required | Notes |
|---|---|---|---|
| IPv4 address | text | Yes | — |
| CIDR prefix length | number | Yes | The number after the slash, from 0 to 32. Accepts 0 or more, up to 32. |
How to use it
- Enter IPv4 address and CIDR prefix length.
- Select Calculate.
Worked example
The address 192.168.1.100 with a /24 prefix.
- Address
- 192.168.1.100
- CIDR
- 24
Mask 255.255.255.0, network 192.168.1.0, broadcast 192.168.1.255. Hosts run .1 to .254 — 254 usable out of 256.
Frequently asked questions
Why does a /24 have 254 usable hosts and not 256?
The all-zeros address identifies the network and the all-ones address is the broadcast. Neither can be assigned to a host.
What is a wildcard mask?
The bitwise inverse of the subnet mask. A /24 mask of 255.255.255.0 has a wildcard of 0.0.0.255, which is the form Cisco ACLs and OSPF use.