Roman Numeral Converter
Convert numbers to Roman numerals and back again.
How to use
- Type a number to see it in Roman numerals.
- Or type a Roman numeral to convert it back to a number.
- Supports values from 1 to 3999.
How the Roman Numeral Converter works
Converts between Arabic numbers and Roman numerals in both directions, covering 1 to 3999.
Converting to Roman works greedily: it repeatedly subtracts the largest value that fits, including the six subtractive pairs. Reading Roman numerals works right to left, adding each value unless it is smaller than the one after it, in which case it is subtracted.
I 1 · V 5 · X 10 · L 50 · C 100 · D 500 · M 1000
subtractive: IV 4 · IX 9 · XL 40 · XC 90 · CD 400 · CM 900
Worked example
2024 breaks into MM (2000) + XX (20) + IV (4), giving MMXXIV.
Things worth knowing
- The system has no zero and no way to write negative or fractional values.
- 3999 (MMMCMXCIX) is the practical maximum, because 4000 would need four M characters. Larger numbers historically used an overline meaning 'times 1000'.
- Only I, X and C are used subtractively, and only before the next two larger symbols. IC for 99 is not valid; XCIX is.
Frequently asked questions
Why only up to 3999?
Standard Roman numerals don't have single symbols above M, so values are usually capped at 3999.
How do subtractive numerals work?
A smaller symbol before a larger one subtracts, like IV for 4 and IX for 9.
Why is 4 written IV rather than IIII?
Subtractive notation keeps numerals short. IIII does still appear on many clock faces, by long-standing convention rather than rule.
How were large numbers written?
With a vinculum — an overline multiplying the numeral by 1,000 — so V̄ meant 5,000.