Free IPv4 and IPv6 subnet calculator: network and broadcast address, usable host range, subnet and wildcard masks, host count and all subnets in the block.
Enter an IP address and a prefix length (CIDR, for example /24) or a subnet mask such as 255.255.255.0. The calculator works out the network address, broadcast address, first and last usable host, the number of hosts, the wildcard mask and every other subnet of that size in the block. It runs entirely in your browser.
A /24 has 256 addresses. The network and broadcast addresses are reserved, leaving 254 usable hosts. Each extra prefix bit halves the block: a /25 gives 126 hosts, a /26 gives 62, a /30 gives 2. A /31 is the exception: point-to-point links use both addresses (RFC 3021).
10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16 are private (RFC 1918) and are not routed on the internet, which is why your device address differs from the public IP shown by What's my IP. 100.64.0.0/10 is shared space used for carrier-grade NAT, and 169.254.0.0/16 means a device failed to get a DHCP address.
IPv6 addresses are 128 bits. A single LAN is normally a /64, a site is usually given a /48 or /56, and fe80::/10 addresses are link-local only. Paste any IPv6 address, full or compressed, and choose a prefix to see the network range and how many addresses it holds.
