Roman numerals

Convert between Roman and Arabic numerals

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What is Roman numerals?

Type a regular number and you'll see it in Roman numerals, or type a Roman numeral like MCMXC and find out what number it is. The tool detects which way you want to convert on its own.

It also shows how the number is built, symbol by symbol, and warns you if a Roman numeral is written incorrectly, for example IIII instead of IV.

How to use it

  1. Enter a number from 1 to 3999 or a Roman numeral.
  2. Read the result in Roman or Arabic numerals.
  3. See the breakdown under “How it's built”.
  4. Copy the result in one click.

Advantages

Technical details

Conversion to Roman numerals uses the greedy algorithm over the table M 1000, CM 900, D 500, CD 400, C 100, XC 90, L 50, XL 40, X 10, IX 9, V 5, IV 4 and I 1. To read a numeral, the canonical form is first validated with the regular expression ^M{0,3}(CM|CD|D?C{0,3})(XC|XL|L?X{0,3})(IX|IV|V?I{0,3})$, which prevents a symbol from being repeated more than three times and only allows I, X and C to be subtracted; then each value is added, or subtracted if the next one is larger. The range is that of classical numerals, from 1 to 3999, without vinculum (overlines) for thousands.

Frequently asked questions

How do you write 2026 in Roman numerals?

2026 is MMXXVI: MM (2000) + XX (20) + VI (6).

What number is MCMXC?

MCMXC is 1990: M (1000) + CM (900) + XC (90).

Why is 4 written IV and not IIII?

In canonical notation a symbol isn't repeated more than three times, so subtraction is used: IV is 5 − 1. The same goes for IX (9), XL (40), XC (90), CD (400) and CM (900).

What is the largest Roman numeral?

With the classical symbols and no overlines, the largest is 3999, written MMMCMXCIX.

Is there a zero in Roman numerals?

No. Roman numerals have no symbol for zero, which is why the tool starts at 1.

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