192.168.1.0/24 ·
10.0.0.0/8 ·
172.16.5.20/23 ·
203.0.113.1/31 ·
2001:db8:abcd::/48
| Prefix | Subnet Mask | Total Addresses | Usable Hosts |
|---|
A subnet calculator takes an IP address and a CIDR prefix or subnet mask and works out everything you need to plan or troubleshoot a network segment: the network address, the broadcast address, the first and last usable host, the number of usable hosts, the total address count, the subnet mask in both dotted-decimal and prefix notation, and the wildcard mask used in access-control lists. It also identifies the IP class and whether the block is private, public, or reserved. This tool supports IPv4 in full, including the special /31 point-to-point (RFC 3021) and /32 host-route cases, and adds IPv6 support with network prefix, first and last address, total address count as a power of two, and both the compressed and fully expanded address forms. Everything is computed instantly in your browser, so no address you type ever leaves your machine.
Type a network in CIDR notation such as 192.168.1.0/24, or an address with a subnet mask such as 10.0.0.5 255.255.255.0, or an IPv6 network such as 2001:db8::/48. Results update live as you type. The URL updates to a shareable link when you submit, so you can bookmark or send a specific calculation. Every value has its own Copy button, or use Copy All Results to grab the whole breakdown at once. A collapsible CIDR reference table lists the mask, total addresses, and usable hosts for every IPv4 prefix.
A /24 gives 256 total addresses but only 254 usable hosts, because the first address is the network address and the last is the broadcast address. The /31 prefix is the exception: under RFC 3021 both addresses are usable, which is why it is common on point-to-point links. A /32 represents a single host route. When borrowing bits to subnet, each additional bit halves the host count and doubles the number of subnets. For IPv6 there is no broadcast address and no need to reserve host addresses, so a /64 still contains 2^64 addresses. Always double-check the wildcard mask when writing firewall or router ACL rules, since it is the bitwise inverse of the subnet mask.
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