how many usable hosts are in a /24?

A /24 has 256 total addresses. Subtracting the network and broadcast addresses leaves 254 usable hosts, which the tool reports directly in the Usable hosts row.

what's the difference between a /31 and a /32 subnet?

A /32 is a single host address with no network or broadcast. A /31, used for point-to-point links per RFC 3021, has two addresses and treats both as usable, since there's no room for a broadcast address.

how do I know if an IP address is private?

Enter the address; the Private (RFC 1918) row checks it against the three private blocks, 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16, and reports yes or no.

what is a wildcard mask and how is it different from a netmask?

A wildcard mask is the bitwise inverse of the netmask, used in Cisco access lists and OSPF configuration instead of a subnet mask. The tool computes it directly from your prefix and shows it alongside the netmask.

IPv4 Subnet Calculator

Compute network, broadcast, netmask, host range and host count from a CIDR, locally.

Local, Runs entirely in your browser, your data never leaves your device.

Loading tool…

Network, broadcast and host range from a CIDR

This tool parses an address written as CIDR (192.168.1.10/24) or as an address and netmask, and computes the netmask, wildcard mask, network and broadcast addresses, first and last usable host, total and usable host counts, the legacy IP class, and whether the address falls inside an RFC 1918 private range. It's the calculation you reach for when sizing a subnet before cutting it, or checking what block an address you were handed belongs to. The masking happens on one 32-bit integer, entirely in your browser.

How to use the IPv4 Subnet Calculator

Enter an address with a CIDR prefix, like 192.168.1.10/24, or as `address netmask`.
Read the network and broadcast addresses computed from your prefix.
Check the first and last usable host and the usable host count.
Look at the IP class and private-range flag to see how the address is categorized.

For a /31, the RFC 3021 point-to-point convention applies: there's no network/broadcast split, so both addresses count as usable. A /32 is a single host and is reported the same way, with total and usable hosts both equal to one.

The private-range check covers exactly the three RFC 1918 blocks: 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16. Addresses outside those, including CGNAT or link-local ranges, are reported as not private.

Frequently asked questions

how many usable hosts are in a /24?: A /24 has 256 total addresses. Subtracting the network and broadcast addresses leaves 254 usable hosts, which the tool reports directly in the Usable hosts row.
what's the difference between a /31 and a /32 subnet?: A /32 is a single host address with no network or broadcast. A /31, used for point-to-point links per RFC 3021, has two addresses and treats both as usable, since there's no room for a broadcast address.
how do I know if an IP address is private?: Enter the address; the Private (RFC 1918) row checks it against the three private blocks, 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16, and reports yes or no.
what is a wildcard mask and how is it different from a netmask?: A wildcard mask is the bitwise inverse of the netmask, used in Cisco access lists and OSPF configuration instead of a subnet mask. The tool computes it directly from your prefix and shows it alongside the netmask.