Developer Tools
CIDR Calculator
CIDR Calculator is a browser-based calculator tool on CalcToolsBase. Free, browser-based CIDR Calculator. Enter your input for an instant, clearly-labelled result - no signup, no uploads. To use it, enter your values and view the result directly in your browser — no signup and nothing to install.
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
The CIDR Calculator is a lightweight, browser-based calculator for when you need to plan an IP network or subnet. It takes an IPv4 address with its prefix, applies bitwise IP arithmetic, and reports the network, mask and host range clearly. Nothing is uploaded and nothing is saved between visits.
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
CIDR when designing a VLAN scheme
CIDR when splitting a block into subnets
CIDR for checking a CIDR range
CIDR 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.