Subnet Calculator
IPv4 subnet calculations
Subnet Calculator: IPv4 subnet calculations. A free, browser-based tool from DevToolbox that runs entirely on your own device: no upload, no account, no tracking.
About the Subnet Calculator
Enter an IPv4 address with a CIDR prefix and get the network address, broadcast address, netmask, wildcard mask, usable host range and host count, calculated in the browser, with no lookup and no disclosure of the network you are planning.
This is a reference and calculation tool, not a probe: the numbers and lookups are computed from tables and arithmetic in your browser rather than by contacting any host. That keeps it usable behind a firewall and means nothing about your network is disclosed.
What you can do with it
- CIDR calculator
- IP subnet
- Network calculator
- Subnet mask
- Host range calculator
How to use it
- Enter the address, code or identifier you want to look up.
- The breakdown is calculated locally from reference tables and arithmetic.
- Every derived field is shown together so you can check your working.
- Copy the result or share the link.
Questions
- Why are two addresses subtracted from the host count?
- The first address in a block is the network identifier and the last is the broadcast address, so neither can be assigned to a host. A /31 is the exception: RFC 3021 allows both addresses on point-to-point links.
- Is my data uploaded anywhere?
- No. The tool is JavaScript that runs in the tab you already have open, and DevToolbox has no backend to send anything to. You can open the network tab and watch: after the page and its script load, nothing is sent while you work.
- Does it work offline?
- Once the page has loaded, yes. The tool needs no network access to do its job, so it keeps working if your connection drops. Reloading the page does need the network unless your browser has it cached.
Related tools
The Subnet Calculator sits in Network & API, one of the 90 tools on DevToolbox.