How to use IPv4 subnet calculator
Calculate an IPv4 CIDR network, mask, broadcast address and usable host range. The check runs when you submit the form. Its inputs are processed in this browser.
How the check works
Enter four decimal octets and a prefix from 0 through 32. Bitwise network arithmetic determines the mask, network and final address in the block.
The Overview tab explains the findings. Measured data lets you search individual fields and values, while JSON report shows the complete export. Export JSON to retain a baseline, or print the findings for your own records. Review the report before sharing it: browser characteristics, token claims, and file names can reveal information about your setup.
Read the result in context
For ordinary subnets the network and broadcast addresses are excluded from the usable range. A /31 is presented as a point-to-point pair under RFC 3021; a /32 is a single address.
Understand the limits
The result is arithmetic, not a scan. Reachability, DHCP assignments and actual routing policy are not checked.
Common questions
Where is the input processed?
In this browser tab. This tool does not submit its input to the site server or a third-party service.
What should I keep with a result?
Record the selected options, browser and time. Review exported values before sharing them. Generated passwords, tokens and HMAC secret keys are excluded from report exports.