IPv4 Subnet Calculator
Enter any IPv4 address and prefix below to get the network address, broadcast address, usable host range, subnet mask, wildcard mask and binary — instantly. It runs entirely in your browser: nothing is sent to any server, and it works offline once loaded.
Try it
How to read the results
Six values come back, and each one answers a different question:
| Value | What it tells you |
|---|---|
| Network address | The first address in the block. It identifies the subnet itself and cannot be assigned to a host. |
| Broadcast address | The last address. Traffic sent here reaches every host in the subnet. Also not assignable. |
| Usable host range | Everything between those two — the addresses you can actually give to devices. |
| Subnet mask | The dotted-decimal form of the prefix (a /26 is 255.255.255.192). |
| Wildcard mask | The inverse of the subnet mask. You need it for ACLs and OSPF. |
| Binary | Where the prefix boundary actually falls. This is the part that makes subnetting click. |
Do the maths yourself (you will need to, in the exam)
A calculator is for speed at work. In the CCNA exam you get no calculator, so learn the block-size method:
- Find the block size: 256 − (the interesting octet of the mask). For a /26, the mask is 255.255.255.192, so the block size is 256 − 192 = 64.
- Count in blocks: the subnets start at .0, .64, .128, .192.
- Locate your IP: 192.168.10.130 falls between .128 and .191, so its network is 192.168.10.128.
- Broadcast: one below the next block — 192.168.10.191.
- Usable hosts: .129 to .190 — that is 2⁶ − 2 = 62 hosts.
Check it against the calculator above. When the two agree every time, you are exam-ready. Drill it with our subnetting practice questions.
Why the −2?
A /26 gives 64 addresses but only 62 usable hosts, because two are reserved: the network address (all host bits 0) and the broadcast address (all host bits 1). Neither can be assigned to a device.
The exception worth knowing: a /31 has no usable hosts by that rule, yet it is used all the time on point-to-point links between routers (RFC 3021), because a link with exactly two endpoints does not need a broadcast address. A /32 is a single host route — used for loopbacks.
Frequently asked questions
How do I calculate a subnet?
Find the block size (256 minus the interesting octet of the mask), count up in blocks to find which one contains your IP, and that block's first address is the network. The broadcast is one below the next block.
What is the difference between a subnet mask and a wildcard mask?
They are inverses. A /26 subnet mask is 255.255.255.192; its wildcard mask is 0.0.0.63. Subnet masks are used on interfaces; wildcard masks are used in ACLs and OSPF network statements.
Why does a /26 have 62 hosts, not 64?
Because the network address and the broadcast address cannot be assigned to devices. The usable host count is 2^(host bits) minus 2.
Is this subnet calculator free?
Yes, completely free with no signup. It runs entirely in your browser, so no data is ever sent to a server.
Sources & further reading
The standards and official documentation behind this page. We link them so you can verify anything here for yourself.
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