This Roman numeral converter works both ways: type an Arabic number to see it in Roman numerals, or type a Roman numeral to find out what number it stands for, from 1 to 3999 (the highest number that can be written with standard Roman notation, MMMCMXCIX).
Besides the result, it includes strict validation: if you type a combination that isn't a real Roman numeral — like “IIII” instead of “IV”, or “IC” instead of “XCIX” — it explains exactly why, instead of trying to guess a number.
How to use
- 1To convert a number to Roman numerals, type it in the first box (between 1 and 3999).
- 2To convert a Roman numeral, type it in the second box; if it isn't valid, you'll see why.
- 3Check the symbol-by-symbol breakdown of each conversion.
- 4Use the reference table for the basic symbols and values.
What you can do
- Two-way conversion
- Validates Roman notation
- Symbol-by-symbol breakdown
How Roman numerals work
Roman numerals are built from seven symbols (I, V, X, L, C, D and M) that are added or subtracted depending on their position. A smaller symbol placed before a larger one is subtracted (IV = 5 − 1 = 4); a repeated symbol or one placed after is added (VI = 5 + 1 = 6). Only a handful of subtractive pairs are valid: IV, IX, XL, XC, CD and CM.
What makes a Roman numeral invalid
Not every sequence of symbols is a correct Roman numeral. Here's what gets checked:
- I, X and C are never repeated more than three times in a row (“IIII” is invalid; it's “IV”).
- V, L and D are never repeated (there's no “VV” or “LL”).
- A symbol can only be subtracted from the next one up in the valid subtraction table (“IC” and “VX”, for example, don't exist).
- Every valid Roman numeral has exactly one correct way to write it.
Where Roman numerals are still used
Roman numerals are still used to number centuries (the 21st century is “XXI”), book chapters and volumes, editions of sporting events (the Olympic Games or the Super Bowl), the numbering of kings and popes (John Paul II), and on some clock faces and movie credits.
Frequently asked questions
How do you write 2024 in Roman numerals?
2024 is MMXXIV: two thousand (MM) plus twenty (XX) plus four (IV).
Why isn't “IIII” a valid Roman numeral?
Because I, X and C can't be repeated more than three times in a row. Four is written IV (subtracting I from V), not IIII.
What's the largest Roman numeral you can write?
With standard notation, the largest representable number is 3999, written MMMCMXCIX. Larger numbers historically used a bar over the symbols, which this tool doesn't support.
Is there a Roman numeral for zero?
No. The Roman numeral system has no symbol for zero, which is why this tool only covers 1 to 3999.