IP subnet calculator (CIDR)

Enter an IP with a prefix (192.168.1.10/24) or an IP with a subnet mask (10.0.0.0 255.255.240.0) to get the network address, broadcast address, subnet mask, wildcard mask, first and last usable host, total and usable address counts, and the binary mask. IPv6 prefixes such as 2001:db8::/48 are supported too.

Everything is calculated locally in your browser. Use it to plan LAN ranges, write router and firewall ACLs, define cloud security-group rules, or check whether two hosts share a subnet.

How to use

  1. Type an IP/prefix or IP and mask.
  2. Results update instantly; use the copy buttons.
  3. The URL contains your input, so you can share it.

FAQ

How many usable IPs are in a /24?

256 addresses, 254 usable hosts. /31 (point-to-point, both usable) and /32 (single host) are special cases.

How do masks map to prefixes?

The prefix is the number of leading 1 bits: 255.255.255.0 = /24, 255.255.240.0 = /20, 255.255.255.252 = /30.

What is a wildcard mask?

The bitwise inverse of the subnet mask, e.g. 0.0.0.255 for a /24, used in Cisco ACLs and OSPF.

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