Roman numerals
Convert numbers to Roman numerals and back - or generate a random one to practise on.
Runs locally in your browser. Nothing you type is ever sent to a server.
Press "Generate" for a random Roman numeral.
Type a number to see it in Roman numerals, or type a numeral to see the number. Press Generate for a random one to practise on. Both directions are exact for every value from 1 to 3,999.
Seven symbols carry the whole system: I is 1, V is 5, X is 10, L is 50, C is 100, D is 500 and M is 1,000. Values are added when written largest first, so XVI is 16. The exception is subtractive notation: a smaller symbol placed before a larger one is taken away instead, which is why 4 is IV and 90 is XC rather than IIII and LXXXX.
There is no standard symbol above M, so the largest number that can be written with the ordinary seven is MMMCMXCIX - three thousand nine hundred and ninety-nine. Larger values historically used an overline to multiply a symbol by a thousand, a notation that does not survive well in plain text, so this tool stops at the standard range rather than inventing something.
You will see IIII on some clock faces and IC written for 99 in casual use. Both can be read, but neither is standard, so the converter rejects them rather than quietly accepting a value it had to guess at. Type the standard form - IV, XCIX - and it converts immediately.
The random number is drawn from your chosen range using your browser's cryptographic random source with rejection sampling, so every value in the range is equally likely. The conversion itself is not random at all - it is the standard greedy algorithm, verified against every number in the supported range.
Type the number in the converter and the Roman numeral appears as you type. It works the other way too - type XIV and you get 14.
3,999, written MMMCMXCIX. Standard Roman numerals have no symbol above M, so larger numbers need an overline notation this tool does not use.
Subtractive notation: a smaller numeral before a larger one is subtracted from it. IIII appears on some clock faces but is not the standard form, and this tool rejects it.
No. The system has no symbol for zero and no way to write negative numbers, which is one reason it was eventually replaced for arithmetic.
Yes. Set a range and press Generate to get a random number shown in both forms, which is how most people practise reading them.
Yes. Every number from 1 to 3,999 has been checked to convert and convert back exactly, and non-standard forms like IIII or IC are rejected rather than guessed at.