Subnet Mask Converter

Subnet Mask Converter is a free online tool. Convert between CIDR prefixes and dotted masks. Enter an IP address or domain and the result appears in seconds. Calculators run offline, and lookups ask public DNS and IP services.

Paste or type your domain or IP address into the Input box. The Convert mode is applied automatically. The result appears instantly in the Result box. Click Copy, or Use as input to keep working with it.

Yes. It is completely free, with no usage limits, watermarks or paid tiers.

No. Open the page and start using it. There is no account, download or browser extension.

Calculators and converters run locally. Lookups send only the domain or IP address you enter to public services such as Cloudflare DNS, Google DNS, Quad9 and ipwho.is, and this site stores nothing.

Subnet Mask Converter has one mode: Convert.

Yes. The layout adapts to any screen size, and the tool works in mobile browsers on iOS and Android.

Current versions of Chrome, Edge, Firefox and Safari. JavaScript must be enabled.

Yes. The result is yours to use in personal and commercial projects without attribution.

There is no fixed limit. Very large inputs depend on your device's memory and may feel slower on older phones.

Click the Copy button above the Result box. For tools that transform text, Use as input moves the result back to the input so you can apply another change.

After the page has loaded, yes. Processing happens in your browser, so the tool keeps working even if your connection drops.

Check that the domain or address is typed correctly, without spaces or extra characters. A network error can also mean an ad blocker or firewall is blocking the lookup service.

DNS answers come straight from public resolvers and reflect what they cache at that moment. IP location data is an estimate, usually accurate to the city or region, never to a street address.

Calculators accept one value at a time unless the tool says otherwise. Lookups work on one domain or IP per request.

Checking DNS records after a website or email change; Finding the provider and region of an IP address; Planning subnets and address ranges; Troubleshooting email delivery with MX, SPF and DMARC.

You may also like What Is My IP Address, IP Address Lookup, DNS Lookup, DNS Propagation Checker. All of them are free and work in the same way.

A public IP address is reachable on the internet and assigned by your provider. Private addresses such as 10.x.x.x, 172.16 to 172.31.x.x and 192.168.x.x are used inside local networks and are not routable on the internet.

It depends on the record's TTL (time to live). Many changes appear within minutes, but resolvers can keep the old answer until the TTL expires, which can take hours for long TTLs.

It is an estimate based on registry and network data. It is usually right about the country and often the city, but it can point to the provider's hub instead of the real location.

Each resolver caches records separately, so right after a change some still return the old value. Comparing resolvers is a quick way to see if a change has spread.

Yes. Tools that show your own IP report the address of the VPN or proxy exit, because that is the address websites see.

Use the contact link in the footer. Bug reports and tool ideas are welcome, and popular requests are added regularly.