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Subnet calculator

Type an IPv4 address with a prefix (192.168.1.10/24) or a mask (255.255.255.0) to see its network, broadcast address, first and last host, how many hosts fit, and whether it’s private.

Prefixes at a glance

Worked out by this page:

PrefixMaskUsable hosts
/8255.0.0.016,777,214
/16255.255.0.065,534
/20255.255.240.04,094
/24255.255.255.0254
/26255.255.255.19262
/28255.255.255.24014
/30255.255.255.2522

Private ranges

10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16 are private (RFC 1918): used inside homes and offices, never routed on the internet. 100.64.0.0/10 is carrier-grade NAT, 127.0.0.0/8 is this computer, and 169.254.0.0/16 is a link-local address a device gives itself when it gets none.

How to use it

  1. Type an address and prefix, or address and mask.
  2. Read the network details; copy what you need.
  3. Check whether another address is in the same subnet.

Questions

Why are two addresses not usable?

The first is the network itself and the last is broadcast. /31 links and /32 single hosts are the exceptions.

Does it do IPv6?

Not yet: IPv4 only.

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