Subnet / CIDR Calculator
Enter an IPv4 address and CIDR prefix to compute the network address, broadcast address, usable host range, subnet mask and host count.
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What is the Subnet / CIDR Calculator?
This calculator breaks an IPv4 CIDR block into its network address, broadcast address, usable host range, wildcard and subnet mask.
How to use it
- 1Enter an IP address such as 192.168.1.10.
- 2Enter a prefix length from /0 to /32.
- 3Read the derived network details.
How it works
The prefix defines how many leading bits are the network. The network address masks off the host bits; the broadcast sets them all to 1. Usable hosts = 2^(32−prefix) − 2 for prefixes ≤ /30.
192.168.1.10/24
Network 192.168.1.0, broadcast 192.168.1.255, usable 192.168.1.1–192.168.1.254 (254 hosts).
Limitations & notes
- IPv4 only.
- /31 and /32 are point-to-point/host routes with special host counts.
Frequently asked questions
How many usable hosts are in a /24, /26 or /28?
Usable hosts equal 2 to the power of the host bits, minus the network and broadcast addresses. A /24 gives 254, a /25 126, a /26 62, a /27 30, a /28 14, a /29 6 and a /30 2. So to fit 50 devices you need at least a /26; a /27 with 30 usable addresses is too small.
What is a wildcard mask used for?
A wildcard mask is the inverse of the subnet mask: 0 bits must match and 1 bits can be anything. Cisco access lists and OSPF network statements use it. For 10.0.5.0/24 the subnet mask is 255.255.255.0 and the wildcard is 0.0.0.255, so an ACL entry would read 10.0.5.0 0.0.0.255. This calculator shows both for any prefix.
Why do /31 and /32 show different host counts?
A /31 has only two addresses. RFC 3021 allows both to be used on point-to-point links between two routers, so the tool reports 2 usable hosts and no separate network or broadcast. A /32 is a single address, used for loopbacks and host routes, and is reported as 1 usable host. Some older devices do not support /31 links.
Which IP ranges are private?
RFC 1918 reserves 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16 for private networks, which are not routed on the public internet. 100.64.0.0/10 is used for carrier-grade NAT, and 169.254.0.0/16 for link-local self-assigned addresses. Entering 172.20.4.9 with a /12 prefix in this calculator shows the full private block, 172.16.0.0 to 172.31.255.255.
Can I paste an address in CIDR notation?
Enter the address and choose the prefix separately: typing 192.168.1.10/24 into the address field is rejected. Any host address works, and the tool finds the network it belongs to, so 192.168.1.130 with /25 returns network 192.168.1.128. It handles IPv4 only and calculates one subnet at a time; it does not split a block into multiple smaller subnets.
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