CIDR Calculator

Enter a CIDR block such as 10.0.0.0/22 to see the IP range it covers, its subnet mask, wildcard mask and how many hosts it holds.

This tool runs entirely in your browser.

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How to use the CIDR Calculator

1Enter an address with a prefix like 10.0.0.5/16, or an address and mask like 10.0.0.5 255.255.0.0.
2Read the network, broadcast, masks and usable host range.
3Optionally choose a longer prefix to split the network into equal subnets.

What is the Subnet Calculator?

The prefix length (/24) says how many leading bits identify the network; the rest identify hosts. A /24 leaves 8 host bits: 256 addresses, of which the first (network) and last (broadcast) are reserved, leaving 254 usable hosts. The subnet mask 255.255.255.0 is the same information written as an address, and the wildcard mask 0.0.0.255 — used in Cisco ACLs and OSPF — is its inverse.

The tool also tells you whether an address is private (10/8, 172.16/12, 192.168/16), loopback, link-local, carrier-grade NAT or public. For IPv6 it shows the first and last address of the prefix and the total count; IPv6 has no broadcast address, and /64 is the standard size for a LAN.

Frequently asked questions

How many hosts are in a /24, /25 or /30?

/24: 254 usable hosts, /25: 126, /26: 62, /27: 30, /28: 14, /29: 6, /30: 2. Each extra prefix bit halves the network.

Why does /31 have 2 usable hosts?

RFC 3021 allows /31 on point-to-point links, where no broadcast address is needed, so both addresses are usable.

Is the Subnet Calculator free and private?

Yes. The Subnet Calculator is free, needs no account, and runs entirely in your browser. What you type is never sent to a server or stored.

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