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Subnet calculator
Network, broadcast, range and usable hosts of an IPv4 block, with the two exceptions almost no calculator explains.
Free, in the browser, no account
With a slash (192.168.1.10/24), with the mask written out (192.168.1.10 255.255.255.0), or just the address — which means /32, that address and no more.
Network
192.168.1.0/24Mask
255.255.255.0Wildcard mask
0.0.0.255Broadcast
192.168.1.255First host
192.168.1.1Last host
192.168.1.254Usable hosts
254Total addresses
256Scope
Private (RFC 1918)Type an address above to check it.
IPv4 only, declared. IPv6 is not "the same with more bits": it abbreviates zeros, has no broadcast, has no reserved network address, and its prefixes count over 128 bits that do not fit in a JavaScript number. Faking it would be worse than not doing it.
Leading zeros in an octet are refused: 192.168.010.1 is read as OCTAL by many system libraries — that is, 192.168.8.1 — so the same text means two different addresses depending on who reads it. That was a real family of vulnerabilities.
Everything happens in your browser: no data is sent anywhere.
How it works
- Type the address and prefix: with a slash, with the mask written out, or just the address.
- Everything you need comes out together, and every value copies with one click.
- There is a second field below: it answers whether another address falls inside this network.
Why it exists
Because you can only do the sum in your head on round prefixes, and round prefixes are the ones that
do not need a calculator. On a /26 or a /23 the question “where does this network end” wants
paper.
And because the two cases where a second opinion really helps are exactly the ones almost no calculator explains.
About the two exceptions
/31 has two usable hosts, not zero. The general formula — total addresses minus two, one for
the network and one for the broadcast — would give zero on a /31. RFC 3021 says those two
addresses are not needed on a point-to-point link: the two ends are all the hosts there are, there is
nobody to broadcast to and no network to name. A calculator that answers “zero” makes people give up
a configuration that works, and that on a backbone with hundreds of point-to-point links saves half
the addresses.
/32 is one address, and it is not a network. It is a host route: a loopback, a static route, a
firewall rule. The first and last host are the address itself, and that is right.
Both show up with their own line of explanation, because anyone meeting them for the first time is wondering whether the calculator is broken — and giving the number without the reason does not settle that.
About masks that are not masks
A valid mask is a block of ones followed by a block of zeros. 255.255.254.0 is fine,
255.255.253.0 is not — and the second gets typed by mistake more often than you would think,
because 253 and 254 look very alike when your head is already elsewhere.
Accepting it would mean computing a network no device would accept. Here it is refused, with the reason written out.
About leading zeros
192.168.010.1 is refused, and that is not pedantry: many system libraries read a number starting
with zero as octal, so 010 is eight. The same text means 192.168.10.1 to one library and
192.168.8.1 to another, and that was a real family of vulnerabilities. There is no right way to
guess which was meant: the only honest answer is not to guess.
About what is not here
IPv4 only, declared. IPv6 is not “the same with more bits”: it abbreviates zeros in its notation, has no broadcast, has no reserved network address, and its prefixes are counted over 128 bits that do not fit in a JavaScript integer. Faking it would be worse than not doing it.
About your data
Everything happens in your browser. This site is made of static files and has no server to send anything to, even if it wanted one.
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