Enter a network and the size of the pieces you want. Get every subnet with its address range and host count — for VLAN plans, VPC layouts and delegating address space.
Runs entirely in your browser — nothing you enter here is sent to a server.
Every extra bit in the prefix cuts a network in half. A /22 holds 1,024 addresses; as /23s it is two networks of 512, as /24s four of 256, as /26s sixteen of 64. The subnets sit side by side with no gaps: each one starts where the previous one ended, on a multiple of its own size. That alignment is what makes the plan easy to route — the original /22 still describes all of them in one line.
Going from /a to /b gives 2b−a subnets. /16 to /24 is 2⁸ = 256.
Each subnet loses two addresses: the network address and the broadcast address.
A /31 is a point-to-point link with two usable addresses (RFC 3021); a /32 is a single host.
AWS, Azure and Google Cloud reserve a few extra addresses in every subnet, so plan a size up.
Size each subnet for what it will hold in a few years, not today, and leave unassigned blocks between the ones you use so that a subnet can grow into its neighbour. Equal-sized subnets, as this tool produces, keep the plan simple and summarisable. When sizes differ a lot — a /30 link next to a /22 of workstations — split in stages: carve the big blocks first, then split one of them again for the small ones. That technique is called variable-length subnet masking, and it is just this operation applied more than once.
256. The prefix grows by 8 bits, and 2⁸ = 256. A /20 contains 16, and a /22 contains 4.
The first address of a subnet identifies the network itself and the last is the broadcast address, so neither can be given to a host. A /24 has 256 addresses and 254 usable hosts.
Yes — split it into large pieces first, then run one of those pieces through the tool again with a longer prefix. This is variable-length subnet masking (VLSM).
The table shows the first 256 and tells you the total and the last one. The counts above the table are always exact.
Upzilla watches hosts on every network you run and tells you which one stopped answering. 10 monitors free.