IP subnet calculator
Network address, broadcast address, host range and mask for an IPv4 subnet.
About this calculator
This IP subnet calculator works out the details of an IPv4 subnet from an address and a CIDR prefix such as /24.
It shows the network and broadcast addresses, the usable host range, the subnet and wildcard masks, and whether the address is private.
How it works
The prefix length says how many leading bits are the network part. The network address keeps those bits and sets the rest to 0, the broadcast address sets the rest to 1, and the hosts lie in between.
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Worked example
- IP address: 192.168.1.130
- Prefix length (CIDR): 26 /
Network: 192.168.1.128/26
Common questions
What does /24 mean?
The first 24 bits are the network and the last 8 are for hosts, the same as a subnet mask of 255.255.255.0. That gives 256 addresses, 254 of them usable.
Why are two addresses not usable?
The first address names the network and the last is the broadcast address. Point-to-point /31 links and single /32 hosts are exceptions.
What are private IP addresses?
Ranges kept for local networks: 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16. They can't be reached directly from the internet.
Sources and further reading
The story behind it
Where the idea came from: CIDR notation, such as /24, was introduced in 1993 to slow the running out of IPv4 addresses.
The original internet split addresses into fixed classes, which wasted millions of them. CIDR let networks be any size, buying years of time until the much larger IPv6 address space arrived.
Why you can trust this calculator
- It runs in your browser. Nothing you type into it is sent anywhere.
- The method is explained on this page, so you can check it yourself.
- Free to use, with no sign-up.
- Results are estimates, so please double-check anything important.
- Spotted a mistake? Tell us and we'll look into it.
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