CIDR Calculator
Calculate CIDR details from an IP and prefix. Get subnet mask, network ID, broadcast address, usable range, and available addresses instantly.
CIDR Calculator
Result will appear here...
SIMILAR TOOLS
What this does
So you have a network written in CIDR notation, something like 192.168.1.0/24, and you need to know what it actually covers: the subnet mask, the network and broadcast addresses, the usable range, and how many hosts fit. This works it all out. Enter the CIDR address, press Convert, and you get the full breakdown.
How to use it
- Type a CIDR address, an IPv4 address followed by a slash and a prefix length, like
10.0.0.0/24. - Press Convert.
- Read the subnet details in the result.
How it works
The tool does the subnet maths from the two parts of your input, the IP address and the prefix length after the slash. The prefix says how many bits at the start of the address are fixed as the network, leaving the rest for hosts. From that it derives the subnet mask, finds the network address, the broadcast address, and the usable host range, all in your browser, with nothing sent anywhere.
Understanding CIDR
CIDR notation is just an IP address plus a number that says how many bits belong to the network. In 192.168.1.0/24, the /24 means the first 24 bits are the network and the remaining 8 are for hosts. The smaller the prefix, the more host bits there are, and the larger the network.
The total number of addresses in a block comes straight from the number of host bits:
total addresses = 2 ^ (32 - prefix)
So a /24 has 2 ^ 8 = 256 addresses. Two of those are reserved in a normal subnet: the first is the network address itself, and the last is the broadcast address, which leaves the rest for actual hosts:
usable hosts = 2 ^ (32 - prefix) - 2
That is why a /24 gives you 254 usable addresses. The network address is the start of the block, the broadcast address is the end, and everything in between is your usable range.
Questions people ask
What does the number after the slash mean?
It is the prefix length, the number of bits at the start of the address that identify the network. A larger number means a smaller network with fewer hosts.
Why are two addresses subtracted from the total?
In a normal subnet, the first address is the network address and the last is the broadcast address, so they are not assigned to hosts. That leaves the total minus two for usable addresses.
What is the broadcast address?
It is the last address in the block, used to reach every host on the subnet at once. It is reserved, so it is not given to an individual device.
Does it support IPv6?
No, this works with IPv4 CIDR notation. The calculations and the 32 bit address size are specific to IPv4.
References
- Internet Engineering Task Force. RFC 4632: Classless Inter-domain Routing (CIDR). https://www.rfc-editor.org/rfc/rfc4632
- Internet Engineering Task Force. RFC 1918: Address Allocation for Private Internets. https://www.rfc-editor.org/rfc/rfc1918
Sugam Baskota is a senior software engineer and Computer Science graduate from UT Arlington, with interests in user scripts, browser extensions, developer tooling, and productivity systems. He spends time building practical utilities and extensions in the kinds of workflows Eon is designed to simplify. At Eon Tools, he reviews useful, password, and developer tools.