IP address to CIDR range Calculator
This calculator converts a range of IPv4 addresses to CIDR range notation or vice versa.
Nothing more, nothing less.
The range-to-IPs conversion only uses the first line of the lower field.
You can also paste a range with a dash in the first field, like 1.2.4.0 - 1.2.5.255.
If you want more info and some extra ranting, scroll down.
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More info
Unlike many similar calculators on other websites, this runs entirely in your local browser, does not phone home, and will not waste your time with a CloudFlare check, asking to identify motorcycles and traffic lights, or worse, try to leech money from you through a paywall. Paying for functionality this simple, which requires only a few dozen lines of script, is plain ridiculous.
(Parasites who make money off this kind of stuff shouldn't worry: with some effort they can rely on SEO to bury this free page deep in search engine results. In other words, as a user, you'd better bookmark this page.)
The only ‘downside’ is that this requires JavaScript (sorry, Lynx users). However, it does not rely on bloated external libraries. This is an early-21st-century-style self-contained webpage that Just Works™. You can use this while offline by saving the HTML file. It may look a little ugly if you don't also save the CSS file, but it will be fully functional.
I do put ads on this page because in the end, hosting bills need to be paid. I would be a hypocrite if I would ask not to use an adblocker, but if you do, a small donation once a year would be appreciated.
Enjoy, and remember: the internet will become as shitty 💩 as you allow big tech companies to enshittify it. Take things back in your own hands, and things may get better.
