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Roman Numeral Converter

Both directions, with malformed numerals named.

Options
Flag non-standard forms
Result

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Seven letters carry values: I is 1, V 5, X 10, L 50, C 100, D 500 and M 1000. A smaller letter before a larger one is subtracted, so IV is 4 and MCMXCIV is 1994.

How to use Roman Numeral Converter

  1. Paste your values. Numerals or numbers, one per line — you can mix them.
  2. Read the conversion. Anything non-standard is named, with the usual form shown.

About converting Roman numerals

Roman numerals encode a number as a sum of seven letter values, largest first, with a limited subtractive shortcut. I is one, V five, X ten, L fifty, C a hundred, D five hundred and M a thousand. Write them in descending order and add them up; the only exception is that a smaller value placed immediately before a larger one is subtracted instead. That exception is narrower than most people assume. Only six subtractive pairs are standard — IV, IX, XL, XC, CD and CM — because a letter may only be subtracted from the next two values above it. This is why 49 is XLIX rather than IL, and 99 is XCIX rather than IC, both of which look plausible and are not conventional. The system also has no zero and no positional notation, which is exactly why it lost to Hindu-Arabic numerals for anything involving calculation. Multiplying MCMXCIV by anything is genuinely difficult, and there is no way to represent an empty column. What it retained is labelling: the numerals are visually distinct from ordinary digits, so a chapter number, a regnal number or a copyright date reads unambiguously as a label rather than a quantity. Historical usage was looser than the modern rules. IIII appears constantly on clock faces, where it visually balances the VIII opposite, and inscriptions show plenty of forms no textbook would accept. Flagging them as non-standard is more useful than rejecting them.

Frequently asked questions

What is the largest Roman numeral?
MMMCMXCIX, or 3,999. The system has no symbol above M, so larger numbers required a bar over a letter to multiply it by a thousand — a convention that was never fully standardised and is not used here.
Why is 4 written IV and not IIII?
The subtractive form became the standard, but IIII was widely used historically and still appears on clock faces, where it balances the VIII opposite it. Both are readable; only IV is conventional in text.
Is there a zero in Roman numerals?
No. The system has no symbol for zero and no concept of positional notation, which is precisely why arithmetic in it is so awkward and why Hindu-Arabic numerals displaced it for calculation while it survived for labelling.
Which subtractive pairs are allowed?
Only six: IV, IX, XL, XC, CD and CM. A letter can only be subtracted from the next two values up, so IL for 49 is not valid — the standard form is XLIX.
Where are Roman numerals still used?
Monarch and pope regnal numbers, film copyright dates, book chapters and front matter, clock faces, and the Super Bowl. All labelling rather than arithmetic, which is the only role the system is well suited to.

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