Skip to content
ToolsOnDuty - free online tools
IP & Network Tools

Subnet Mask Converter

Convert IPv4 subnet masks and CIDR prefixes in either direction.

Free browser toolRuns in your browserNo sign-up

IP & Network Tools

Subnet Mask Converter

Convert a dotted IPv4 subnet mask to CIDR notation, or convert a CIDR prefix back to its mask.

Calculation runs locally in your browser. No address is uploaded.

About the Subnet Mask Converter

Subnet Mask Converter is a focused network utility for administrators, developers, support teams and people troubleshooting an internet connection. Convert IPv4 subnet masks and CIDR prefixes in either direction.

The calculation runs locally in your browser, so the address is not uploaded.

Results describe public network information and should not be treated as proof of a person's identity or exact physical location.

Key features

  • Dotted mask to CIDR
  • CIDR to subnet mask
  • Wildcard and binary masks

How to use

  1. 1Enter a dotted mask or CIDR prefix.
  2. 2Select Convert.
  3. 3Copy the equivalent mask, prefix or wildcard value.

Examples

Subnet Mask Converter example
Input: 255.255.255.0
Output: /24

Only contiguous IPv4 masks are valid subnet masks.

Frequently asked questions

Is this tool free?
Yes. It requires no account, payment or software installation.
Are IP location results exact?
No. IP geolocation is approximate and usually identifies a network region, not a home, person or precise device location.
Does this tool expose private network data?
No. This calculator operates entirely on the values in your browser.
Can I use it on mobile?
Yes. Inputs, tables and results adapt to phones, tablets and desktop browsers.

Continue your workflow

Open a related tool to prepare your files or refine the finished result.