IP Subnet Calculator (IPv4 CIDR)

An IPv4 subnet is a block of addresses that share the same leading bits. Type an address with its prefix (/25) or its mask (255.255.255.128) and this calculator works out the network and broadcast addresses, the range you can give to hosts, how many hosts fit, the subnet and wildcard masks in dotted, binary and hex form, and what kind of address it is (private, public, loopback, carrier-grade NAT, documentation…). It can also split the network into smaller subnets.

How to use this tool

1. Type an address such as 192.168.1.130/25, or an address and mask separated by a space.
2. For a bare address, pick the prefix length from the list.
3. Optionally choose a longer prefix under "Split into subnets of" to list the smaller networks.
4. Copy the network, host range and masks you need.

Formula

mask = 2³² − 2^(32 − p) · network = IP AND mask · broadcast = network OR wildcard · usable hosts = 2^(32 − p) − 2

p is the prefix length and the wildcard mask is the mask with every bit inverted. A /31 is a special case: RFC 3021 lets both of its addresses be used on point-to-point links, and a /32 is a single host.

Example

192.168.1.130/25: the mask is 255.255.255.128, so the last 7 bits belong to hosts and the block holds 2⁷ = 128 addresses. 130 AND 128 = 128, so the network is 192.168.1.128 and the broadcast 192.168.1.255. Hosts run from 192.168.1.129 to 192.168.1.254 — 126 usable hosts. The wildcard mask is 0.0.0.127.