Easy Subnet Calculator

Type an IPv4 address with a /prefix or a subnet mask and read back the network, broadcast, host range and how many hosts fit, before you press anything.

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One box, any notation. The host count comes first because it is what you came for.

Drag the prefix and every number moves with it — /24 down to /26 in one gesture.

The mask in binary, with the network bits and the host bits colored apart.

Private, loopback, link-local, CGNAT, documentation — thirteen ranges named on sight.

Right on a /31 and a /32, where subtracting two from everything gives nonsense.

One box, any notation. The host count comes first because it is what you came for.

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See it in action

A subnet calculator that answers as you type

A subnet calculator gets opened for one of a handful of questions. How many devices will this range hold? Where does the network start and end? What mask goes in the router? Easy Subnet Calculator puts all of those on one screen and works them out on every keystroke.

There is a single input. It takes 10.0.4.17/22, 10.0.4.17 255.255.252.0, 10.0.4.17/255.255.252.0, or a bare address that keeps the prefix already showing. The first figure under it is the usable host count in large type, followed by the host range and what kind of address you typed.

The rows below give Network, Broadcast, Netmask, Wildcard, First host, Last host and the total number of Addresses, each with its own copy button for pasting into a config or a ticket.

Everything is IPv4. An entry it cannot read gets a plain error message in place of results rather than a guess, and whatever you last typed is back in the box the next time you open the window.

Subnet mask calculator with a prefix length slider

The Prefix length slider runs from /0 to /32. Drag a /24 to /26 and every row moves with it: 254 usable hosts become 62, the broadcast drops from .255 to .63, and the mask changes to 255.255.255.192. It turns the common sizing question, will 40 machines fit in this block, into a glance rather than a sum.

Under Written as in Settings you choose how the mask is shown: 255.255.255.0 and /24, the dotted form only, or the /24 form only. Switch on Show hexadecimal for hex values beside the network, broadcast, netmask and wildcard, the form an access list or router config often wants.

How to calculate a subnet by hand, and check it

Working a subnet out on paper takes four steps, and the app shows the result of each one, so it doubles as a way to check homework or an exam answer:

Write the mask as 32 bits: the prefix length in 1s, then 0s. A /26 is 26 ones and 6 zeros, or 255.255.255.192.
AND the address with the mask to find the network address.
Set every host bit to 1 to find the broadcast address.
Raise 2 to the number of host bits and subtract 2 for the usable hosts: 2 to the 6th is 64, so a /26 holds 62.

CIDR notation in binary: where the prefix cuts

With Show the address in binary on, the address and the netmask are written out bit by bit, with the network bits and the host bits colored apart. That is the diagram a networking course draws to explain CIDR, and seeing a /27 split the last octet three bits in makes subnetting easier to reason about than a cheat sheet.

Private IP address ranges and other special blocks

Say what kind of address it is labels the input on sight, so an unfamiliar address explains itself:

Private (RFC 1918): 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16
Carrier-grade NAT (RFC 6598): 100.64.0.0/10
Loopback 127.0.0.0/8 and Link-local (APIPA) 169.254.0.0/16
Documentation TEST-NET-1, -2 and -3, and Benchmarking (RFC 2544)
Multicast, Reserved for future use, This network and Limited broadcast
Anything else is marked Public, with its historical class beside it

What it shows

Usable hosts first, with the first to last host range under it
Network, broadcast, netmask, wildcard and total address count
A copy button on every row
A /31 shown as a point-to-point link with two usable hosts and no broadcast
A /32 shown as a single host
Non-contiguous masks such as 255.0.255.0 refused rather than guessed at
The last address you typed restored when you reopen it
Match Windows, Light or Dark theme

Questions

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Does it calculate IPv6 subnets?

No. It works with IPv4 addresses only, and an IPv6 address is rejected as not an IPv4 address.

Can I type a subnet mask instead of a CIDR prefix?

Yes. It accepts 192.168.1.1/24, 192.168.1.1 255.255.255.0, 192.168.1.1/255.255.255.0, or a bare address, which keeps the prefix already on screen. A mask whose 1 bits are not contiguous, such as 255.0.255.0, is refused.

How does it handle /31 and /32?

A /31 is treated as a point-to-point link with no network or broadcast address and two usable hosts. A /32 is shown as a single address.

Can it split a network into smaller subnets?

No. It shows one subnet at a time. The prefix slider, from /0 to /32, lets you see how the network, range and host count change as you move it.

Does it show the wildcard mask and hex values?

Yes. The wildcard mask is always shown, and a setting adds hexadecimal for the network, broadcast, netmask and wildcard. You can also have the mask written as dotted, as a /prefix, or both.

Which special address ranges does it recognize?

Thirteen, including the three RFC 1918 private ranges, loopback, link-local, carrier-grade NAT, the three documentation blocks, benchmarking and multicast, plus the limited broadcast address. It also shows the historical class, A to E.

How many usable hosts are in a /24 subnet?

254. A /24 has 256 addresses, and the network and broadcast addresses are not assignable. Each extra prefix bit halves that: a /25 holds 126, a /26 holds 62 and a /30 holds 2.

What is a wildcard mask?

The inverse of the subnet mask: the host bits set to 1 instead of the network bits. For 255.255.255.0 it is 0.0.0.255. It is shown on its own row for every subnet.

How do I convert CIDR to a subnet mask?

Write the prefix as that many 1 bits followed by 0 bits and read it in four 8-bit groups, so /22 becomes 255.255.252.0. Type any address with the prefix and the Netmask row shows it.

Which versions of Windows does it run on?

Windows 10 (version 1809 or later) and Windows 11.

Is it a subscription?

No. Easy Subnet Calculator is a one-time purchase of $1.99, and updates are included.

How do I get it?

Buy it on this page and your license key arrives by email. If the button says Notify me, Easy Subnet Calculator is not on sale here yet; leave your email and we will tell you when it is.