Turn a number into Roman numerals or read one back, anywhere from 1 to 3999. The numeral box only accepts the standard form: IIII and IC are reported as errors rather than quietly read as 4 and 99, because if you typed one by accident you want to be told.
Runs entirely in your browser
Convert numbers to Roman numerals and back, for anything from 1 to 3999 (the range the standard numerals cover without special notation). Type a number to see its numeral form, or type a numeral to read its value — useful for dates, clock faces, book chapters, film credits and the perennial “what year is this tattoo?”.
What sets it apart is that it validates the numeral form strictly. Non-standard writings like IIII (instead of IV) or IC (instead of XCIX) are reported as errors rather than quietly interpreted, because if you typed one by mistake you want to know. Reading them silently would hide a typo behind a plausible-looking answer.
It runs in your browser, so conversions are instant and private. Use it to write a date in numerals correctly, to decode one you have found, or to check that a numeral you wrote is actually valid.
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