Subnet Calculator

What each value means

• Network address — the first address in the subnet, used to identify the subnet itself. It's never assigned to a device.
• Broadcast address — the last address in the subnet, reserved for sending a message to every host on it. It's also never assigned to a device.
• Usable host range — every address between the network and broadcast address, the ones that can actually be assigned to a device.
• Subnet mask / CIDR — two ways of writing the same thing: how many bits of the address are the network portion. A /26 prefix is the same as a 255.255.255.192 mask.
• Wildcard mask — the inverse of the subnet mask, used by access control lists and routing protocols like OSPF instead of a normal subnet mask.

For a /30 and smaller you'll notice the usable host count is always two less than the total number of addresses — that's the network and broadcast address getting subtracted out. A /31 is a special case used for point-to-point links where both addresses are usable, and a /32 identifies a single host.

Worked example

The calculator above starts with 192.168.1.130 /26 loaded in, so here's what it did with those values. A /26 prefix is a 255.255.255.192 subnet mask, which leaves 6 host bits and puts 64 addresses in every subnet on that network. Counting up by 64 in the last octet gives subnet boundaries at 0, 64, 128, and 192 — 130 falls between 128 and 192, so it's part of the 128 subnet.

• Network address: 192.168.1.128 — the start of that subnet
• Broadcast address: 192.168.1.191 — one less than the next subnet (192)
• Usable hosts: 192.168.1.129 through 192.168.1.190, 62 addresses in total

Change the IP address or prefix in the fields above and hit Calculate to see the same breakdown for your own values.

Quick reference

CIDR notation vs. dotted-decimal subnet masks

A subnet mask and a CIDR prefix describe the exact same thing two different ways — both say how many of the address's 32 bits belong to the network portion. 255.255.255.192 written in binary is 26 one-bits followed by 6 zero-bits, which is exactly what /26 means. Networking gear and documentation use both interchangeably, so this calculator (and the practice problems) accept either one in the same field.

Dotted-decimal masks only ever contain the values 255, 254, 252, 248, 240, 224, 192, 128, or 0 in each octet — if you see anything else, it's not a valid subnet mask.

Public and private IP address ranges

Not every IPv4 address is routable on the public internet. RFC 1918 sets aside three ranges for private networks — the ones you'll find behind almost every home router and school network:

• 10.0.0.0 – 10.255.255.255 (a full Class A block, 10.0.0.0/8)
• 172.16.0.0 – 172.31.255.255 (172.16.0.0/12)
• 192.168.0.0 – 192.168.255.255 (192.168.0.0/16)

Everything else — outside of a handful of other reserved ranges like loopback (127.0.0.0/8) and multicast (224.0.0.0/4) — is public address space. The calculator's "Address class / type" row flags which of these an address falls into.

Frequently asked questions

Want to build this skill instead of just checking an answer? The subnetting practice problems page explains the manual method step by step and then generates random problems for you to work through. Once that's comfortable, VLSM practice applies the same math to fitting several differently-sized subnets into one address block.