Roman Numeral Converter
Convert between Roman numerals and ordinary numbers, from I to MMMCMXCIX. Rejects malformed numerals such as IIII or IC instead of guessing.
Result
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Reference
Files are processed in your browser and are never uploaded to a server.
How to use
Free to use with no sign-up, no install and no usage limit.
Enter a number to get the numeral, or a numeral to get the number. The direction switches with the tabs and the result updates as you type.
Reading a numeral is easy to get wrong in a way you never notice. Adding up the letters happily accepts IIII, VV and IC, which are not valid numerals at all. Here the value is written back out and compared with what you typed, so anything that does not round-trip is reported rather than accepted.
The supported range is 1 to 3999. Larger numbers need an overbar to mark thousands, a notation with several competing conventions and patchy font support, so this tool says it cannot do them instead of inventing a form.
Lowercase input and surrounding spaces are fine. The reference table below covers the letters and the subtractive pairs that cause most of the confusion.
Nothing you type is sent to a server. The conversion happens inside your browser.