IPv4 subnet calculator (CIDR)
Enter an IPv4 address and a prefix length such as /24 to get every subnet detail you need when planning a network or configuring devices.
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Processing and privacy: The result is calculated inside your browser and your data is not sent to any server.
How to use it
- Enter ipv4 address and prefix length (cidr).
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
Mask = 2^32 minus 2^(32 minus prefix). Network = address AND mask; broadcast = network OR inverted mask. Total = 2^(32 minus prefix); usable = total minus 2, except /31 = 2 (RFC 3021) and /32 = 1.
Example
Inputs: IPv4 address = 10.20.30.40, Prefix length (CIDR) = 13 /. Result: Network address: 10.16.0.0; Usable hosts: 524,286; Total addresses: 524,288.
10.20.30.40
10.16.0.0
Limits and caveats
- IPv4 only; use the IPv6 expander for IPv6 addresses.
- /31 counts 2 usable hosts per RFC 3021; some older devices do not support it.
Questions about this tool
Why are usable hosts 2 fewer than total addresses?
The first address names the network and the last is the broadcast, so neither goes to a device. /31 and /32 are the exceptions.
What is a wildcard mask?
It is the inverted subnet mask, used by Cisco access lists and OSPF to match address ranges.
How many hosts fit in a /24?
A /24 has 256 addresses, of which 254 are usable.