Time/Numbers
Roman Numeral Converter
Arabic number ↔ Roman numeral. Type into either field and the other updates automatically.
Roman numerals write a number using combinations of the letters I, V, X, L, C, D, M under an additive-subtractive rule: a smaller letter before a bigger one is subtracted (IV = 4), and after it, added (VI = 6). This tool converts in both directions instantly.
How to use it
- Enter an Arabic number in one field and its Roman form appears automatically in the other.
- Enter a Roman numeral and the Arabic number is recognized instantly, with a check for a valid notation.
- An invalid letter combination (like IIII instead of IV, under the standard rule) is flagged as an error.
Common uses
- Decoding Roman numbering on book chapters, building cornerstones, or movie credits.
- Writing an edition, chapter, or paragraph number in the traditional Roman format.
- A teaching example of positional vs. non-positional numeral systems when studying the history of mathematics.
Things to keep in mind
Standard Roman notation has no symbol for zero and doesn't support numbers above 3999 without special marks (a bar over a letter to multiply it by 1000).
IIII instead of IV on clock faces is a long-standing decorative tradition for symmetry with VIII, not a mistake or an exception to the rules.
Article about this tool: Roman numerals: how a system with no zero and no place value works
Frequently asked questions
Why is only the range from 1 to 3999 supported?
Classical Roman notation has no symbol for zero or negative numbers, and the largest basic digit M (1000) without special marks allows numbers only up to 3999 (MMMCMXCIX) to be written correctly.
What is subtractive notation, and why IV instead of IIII?
The subtraction rule allows writing a smaller symbol before a larger one instead of four identical symbols in a row: IV (4) instead of IIII, IX (9) instead of VIIII. This makes the notation shorter and unambiguous.
Can I enter Roman numerals in lowercase?
Yes, the tool recognizes lowercase letters, but the result always shows the canonical notation in uppercase, as is standard.
How were Roman numbers above 3999 historically written?
Historically, a bar (vinculum) drawn over a symbol multiplied its value by 1000 for larger numbers — for example, a barred X meant 10,000. This notation is rare and isn't part of the modern common standard, so most Roman numeral calculators, including this one, don't support it.
Why do clock faces sometimes show IIII instead of IV?
That's a decorative tradition, not an error — clock faces have long used the additive IIII for visual symmetry with VIII on the opposite side, even though the subtractive IV was already used in texts of the same period.