In short: An IP subnet calculator takes an IPv4 address and prefix length (CIDR, such as /24) and returns the network address, broadcast address, netmask, usable host range and host count.
About IP Subnet Calculator
Subnetting splits an IP range into smaller networks. The prefix length after the slash in CIDR notation, such as /26, says how many leading bits identify the network; the remaining bits number the hosts. A /26 leaves 6 host bits, giving 64 addresses, of which 62 are usable because the first is the network address and the last is the broadcast address.
This calculator handles every prefix from /0 to /32, including the special cases /31 (two usable addresses for point-to-point links, per RFC 3021) and /32 (a single host). It also tells you whether the address is private (RFC 1918), loopback, link-local, CGNAT or multicast.
How to use IP Subnet Calculator
- Type an IPv4 address with a prefix, such as
10.0.0.17/20, or an address and netmask like10.0.0.17 255.255.240.0. - Or type just the address and pick a prefix from the list.
- Read the network details; values update as you type.
Examples
192.168.1.10/24: network 192.168.1.0, broadcast 192.168.1.255, hosts .1–.254, 254 usable.
192.168.1.130/26 sits in the third of four /26 blocks: network 192.168.1.128, hosts .129–.190, broadcast .191.
Frequently asked questions
Why are two addresses not usable?
In a normal subnet the lowest address identifies the network and the highest is the broadcast address. /31 and /32 are exceptions.
What is a wildcard mask?
The inverse of the netmask (for /24, 0.0.0.255). Cisco ACLs and OSPF configuration use it.
Does it support IPv6?
Not yet; this calculator covers IPv4.
Which ranges are private?
10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16 (RFC 1918). 100.64.0.0/10 is shared address space used by carrier-grade NAT.
Updated November 2026 · Free, no signup · How we build and test tools