Subnet Calculator
IPv4 and IPv6 subnet from an address and prefix: network, broadcast, mask, wildcard, host range, usable hosts, binary view, and a split into smaller subnets.
The network and broadcast addresses, first and last host, host count, mask and wildcard for any CIDR, the address in binary with the split marked, and the list of subnets when you carve it up.
Example: 192.168.10.37/24 is in 192.168.10.0/24: hosts .1–.254 (254), broadcast .255, mask 255.255.255.0; split into /26 gives four subnets of 62 hosts.
Address AND mask,
nothing else.
How a prefix length becomes a mask, where the network and broadcast addresses come from, why /31 and IPv6 are different, and what the page does not know about your network.
Prefix, mask and network
A /24 means the first 24 bits identify the network and the remaining 8 the host. The mask has those 24 bits set (255.255.255.0); AND-ing the address with it clears the host bits and gives the network address; OR-ing with the wildcard (the inverted mask) sets them and gives the broadcast. The binary view shows the address with a bar at the boundary so you can see the split rather than trust it.
How many hosts
An IPv4 block of prefix p holds 2^(32 − p) addresses; the first is the network and the last the broadcast, so 2^(32 − p) − 2 are usable. Two exceptions per RFC 3021: a /31 on a point-to-point link uses both addresses, and a /32 is a single host. IPv6 has no broadcast and reserves nothing at the ends, so a /64 holds all 2^64 = 18,446,744,073,709,551,616 addresses — the page keeps these as exact integers.
Splitting a block
Carving a /24 into /26 blocks means borrowing 2 host bits: 2² = 4 subnets of 2⁶ = 64 addresses each, laid out at fixed steps from the network address. The page lists the first eight and the total. The same works in IPv6 — a /48 site prefix gives 65,536 /64 LANs.
What the number does not settle
The range labels (private, link-local, unique local, multicast) come from the IANA special-purpose registries and are informational. Whether the block is routed, who assigns it, which address is the gateway, and how VLSM is laid out across a site are your network’s decisions. Inputs stay in your browser; the same four anonymous usage counts as the rest of the site apply.
SOURCES
- RFC 4632 — Classless Inter-domain Routing (CIDR)
- RFC 3021 — Using 31-bit prefixes on IPv4 point-to-point links
- RFC 4291 — IP Version 6 Addressing Architecture
- IANA IPv4 Special-Purpose Address Registry
Last reviewed 18 September 2026. How results are checked: How we verify.