Enter any IPv4 address and CIDR prefix or dotted subnet mask like 255.255.255.0. Network address, broadcast, host range, and wildcard mask calculate instantly. The built-in visual subnet calculator lets you split and rejoin blocks interactively.
Enter an IP address and prefix above to calculate
VLANlab's IPv4 subnet calculator computes all subnet properties from an IP address and prefix length (CIDR notation) or dotted subnet mask. It instantly returns the network address, broadcast address, first and last usable host, subnet mask, wildcard mask, total host count, and usable host count.
The Visual Block Diagram shows your subnet as a proportional address space bar - the network address, usable host range, and broadcast address are each colored to scale, so you can immediately see how large the host space is relative to the total block. The CIDR hierarchy strip below it shows which parent prefixes contain your subnet, helping you understand the addressing context at a glance (for example, how a /26 sits inside a /24 inside a /22).
The built-in subnet divider lets you split any network into smaller subnets interactively - divide a /16 into /17s, /18s, or any smaller prefix. Join subnets back, export the full table as CSV, and share the exact layout via a bookmarkable URL. Binary representation shows exactly which bits are network bits versus host bits.
Enter the prefix as CIDR notation (/24) or as a dotted subnet mask (255.255.255.0). The IP address can be any valid IPv4 address - the calculator automatically derives the network address from the host bits.
Subnetting divides a larger IP address block into smaller, routable subnetworks. Network engineers use subnetting to allocate address space efficiently, reduce broadcast domains, and implement network segmentation. CIDR (Classless Inter-Domain Routing) notation expresses both the IP address and the prefix length in a single value - for example, 192.168.1.0/24.
A /26 leaves 6 host bits, so each block holds 64 addresses and the mask is 255.255.255.192. The blocks start at .0, .64, .128 and .192, and 77 falls in the block that starts at 64. So the network address is 192.168.10.64, the broadcast address is 192.168.10.127, and the 62 usable hosts run from 192.168.10.65 to 192.168.10.126.
Before CIDR (1993), the first bits of an address fixed the size of its network: class A (first octet 1 to 126) used /8, class B (128 to 191) /16 and class C (192 to 223) /24. CIDR dropped the classes, so an address alone no longer says where its network ends, and the prefix or mask always goes with it. The old names live on as shorthand for /8, /16 and /24 networks.