Roman Numeral Converter
Type a number or a Roman numeral — get the other instantly, with the breakdown.
Standard letters I V X L C D M cover 1–3,999; a vinculum (overline ×1,000) reaches 3,999,999.
Reading and writing Roman numerals
Roman numerals build every number from seven letters, each with a fixed value: I = 1, V = 5, X = 10, L = 50, C = 100, D = 500, and M = 1000. You normally write them from largest to smallest and add the values up, so MMXV is 1000 + 1000 + 10 + 5 = 2015. The one twist is subtractive notation: when a smaller letter sits directly before a larger one, you subtract it instead. That is why 4 is IV (5 − 1) rather than IIII, and 9 is IX. This converter applies those rules in both directions and shows a step-by-step breakdown so you can see how each letter contributes.
The rules that keep numerals valid
Only six subtractive pairs are allowed, and a letter may repeat at most three times in a row. Those two constraints are what rule out forms like IIII or IC. The table lists everything you need to compose any standard numeral.
| Symbol | Value | Subtractive pair | Means |
|---|---|---|---|
| I | 1 | IV / IX | 4 / 9 |
| V | 5 | — | — |
| X | 10 | XL / XC | 40 / 90 |
| L | 50 | — | — |
| C | 100 | CD / CM | 400 / 900 |
| D | 500 | — | — |
| M | 1000 | — | — |
What the system cannot express
The Roman system has no zero, no negative numbers, and no fractions of a unit, because it was designed for counting and tallying rather than place-value arithmetic. The smallest value you can convert is therefore 1. If you enter 0, a minus sign, or a decimal point, the tool tells you clearly rather than guessing at a meaning that does not exist.
Reading the other direction is just as strict. On the Roman → Number tab the converter accepts letters in either case and ignores stray spaces, but it still checks that the numeral is properly formed: a repeated letter beyond three in a row, or an invalid subtraction such as IL or VX, is reported as an error instead of being silently accepted. That way a malformed numeral copied from somewhere else is caught rather than turned into a misleading number.
Where you still see them
Roman numerals remain common on clock and watch faces, building cornerstones and dedication dates, book and chapter numbers, film and television copyright lines, monarch and pope names, and event editions such as the Super Bowl (Super Bowl LVIII is number 58). To write a year, convert it on the Number → Roman tab and copy the result; to read a numeral you have found, paste it on the Roman → Number tab and the tool decodes it and confirms whether it is validly formed.
Sources & further reading
Frequently asked questions
How do Roman numerals work — what do I, V, X, L, C, D, M mean?
Each letter is a fixed value: I = 1, V = 5, X = 10, L = 50, C = 100, D = 500 and M = 1000. You add letters from largest to smallest (MMXV = 2015), but when a smaller letter sits before a larger one you subtract it — this is subtractive notation, which gives IV = 4, IX = 9, XL = 40, XC = 90, CD = 400 and CM = 900. This Roman numeral converter builds and validates every numeral by those exact rules.
Why is there no zero — and no negative or decimal Roman numerals?
The Roman system has no symbol for zero and no way to write negative numbers or fractions of a unit, because it was made for counting and tallying rather than place-value arithmetic. So the smallest value you can convert is 1 (I). Enter 0, a minus sign or a decimal point and the tool tells you clearly instead of silently guessing.
What is the largest Roman numeral — can I go past 3,999?
With the standard letters the practical maximum is 3,999 (MMMCMXCIX), because there is no single symbol larger than M. To write bigger numbers, scribes used the vinculum — an overline that multiplies a numeral by 1,000. This converter uses vinculum notation to reach 3,999,999, so 5,000 becomes V with a bar (V̅) and 1,000,000 becomes M with a bar (M̅).
How do I write a year or date in Roman numerals?
Convert the whole number: 2026 = MMXXVI, 1994 = MCMXCIV, 2000 = MM. That is exactly how years appear on clock faces, building cornerstones, book chapters, movie and TV copyright credits and the Super Bowl (Super Bowl LVIII = 58). Type the year on the Number → Roman tab and copy the result, or paste a numeral on the Roman → Number tab to read a date you found.
Is my input sent to a server?
No. Every conversion runs entirely inside your browser in plain JavaScript — nothing you type is uploaded, logged or tracked, and there are no ads. Once the page has loaded it even works offline, so you can convert Roman numerals privately with no connection at all.