Developer Tools
CIDR Calculator
CIDR — CIDR Calculator parses the IPv4 address and prefix and derives the network, broadcast, mask and host range with bitwise arithmetic. This page runs that same calculation on your numbers, in your browser: no signup, no uploads, nothing stored.
Enter an IPv4 address with its prefix and CIDR Calculator works out the network, mask and host range with bitwise IP arithmetic — fast, free and private, with no sign-up or uploads.
Browser-side developer and utility helpers for everyday and learning use. Everything runs locally in your browser and nothing you enter is uploaded. Validate production or security-critical output with trusted, official tools before relying on it.
About this tool
CIDR Calculator parses the IPv4 address and prefix and derives the network, broadcast, mask and host range with bitwise arithmetic. That is the whole of the calculation — the mistakes happen in the inputs. It matters when a format, encoding or size has to be exactly right for the system reading it. Worked example: The CIDR block 192.168.1.0/24 has a 255.255.255.0 mask and 2 (32−24) = 256 addresses (254 usable hosts). Use the calculator with your own figures; it runs entirely on your device.
How to use
- Type an IPv4 address followed by a slash and prefix.
- Check that each octet is between 0 and 255.
- Run the calculator to analyse the block.
- Read the network, broadcast, mask, and host details.
Why use the CIDR Calculator
Instant
Each result is computed on your device the moment you run the tool.
Private
The text and numbers you enter stay in your browser and are never uploaded.
Free
No signup and no paywall to use any tool in this set.
Works offline
Once the page has loaded it keeps working on a weak or dropped connection.
Built for developers
Plain inputs and outputs you can copy straight into code, configs, or notes.
Honest by design
Conversions and heuristics are for everyday and learning use; verify security-critical output with trusted, official tools.
Common uses
Use it when designing a VLAN scheme
Use it when splitting a block into subnets
Use it for checking a CIDR range
Use it for troubleshooting an IP range
CIDR in network-engineering coursework
CIDR in firewall and routing setup
Technical notes
CIDR Calculator parses the IPv4 address and prefix and derives the network, broadcast, mask and host range with bitwise arithmetic.
Results are reference values; validate against your own environment before relying on them in production.
Results are rounded for display; the underlying calculation keeps full precision.
Worked example
The CIDR block 192.168.1.0/24 has a 255.255.255.0 mask and 2(32−24) = 256 addresses (254 usable hosts).
FAQ
How are slash 31 and slash 32 handled?
A slash 32 is treated as a single-host route, and a slash 31 is treated as a two-address point-to-point link following RFC 3021, rather than using the usual host range.
Does it validate the IP address?
Yes. Each octet must be a whole number from 0 to 255 and the prefix must be from 0 to 32, otherwise the entry is rejected.
What is the wildcard mask?
The wildcard mask is the bitwise inverse of the netmask and is often used in access-control lists.
Why are two addresses subtracted for usable hosts?
In a normal subnet the network and broadcast addresses are reserved, so the usable host count is the total minus those two.