IP Subnet Calculator

Enter an IPv4 address and a CIDR prefix (or subnet mask) to get the network and broadcast addresses, wildcard mask, usable host range, host counts and the address class — all live. Everything runs in your browser; nothing is sent anywhere or stored.

How to use the subnet calculator

  1. Type an IPv4 address such as 192.168.1.10.
  2. Pick a CIDR prefix from /0 to /32, or type a subnet mask — the two stay in sync automatically.
  3. Read off the network, broadcast, host range and counts. Results update as you type.

Common prefixes: /24 is 255.255.255.0 (254 usable hosts), /25 is 255.255.255.128 (126 hosts), /26 is 255.255.255.192 (62 hosts) and /30 is 255.255.255.252 (2 hosts, a point-to-point link).

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Frequently asked questions

What is a subnet mask and CIDR prefix?

A subnet mask splits an IPv4 address into a network part and a host part. The CIDR prefix (for example /24) is the shorthand for how many leading bits belong to the network — /24 equals a mask of 255.255.255.0. The remaining bits identify hosts inside that network.

What are the network and broadcast addresses?

The network address is the first address in the block (all host bits 0) and names the subnet itself. The broadcast address is the last address (all host bits 1) and reaches every host on the subnet. Neither can normally be assigned to a device, which is why usable hosts are two fewer than the total.

What is a wildcard mask?

A wildcard mask is the bitwise inverse of the subnet mask — where the mask has 1 the wildcard has 0, and vice versa. For 255.255.255.0 the wildcard is 0.0.0.255. It is used by routers and access lists (for example Cisco ACLs) to match a range of addresses.

How are usable hosts calculated?

For a prefix of /n there are 2^(32 - n) total addresses. Usable hosts are total minus 2 (network and broadcast are reserved). The exceptions are /31, which defines a 2-address point-to-point link with no reserved addresses, and /32, a single host.

Which address ranges are private?

RFC 1918 reserves three private ranges: 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16. Addresses outside these (and other reserved blocks) are treated as public. This tool also flags loopback 127.0.0.0/8 and link-local 169.254.0.0/16.

Is my data sent anywhere?

No. Every calculation runs entirely in your browser using plain JavaScript — nothing is uploaded to a server and nothing is stored. You can use it offline once the page has loaded.