Converters
Roman numeral converter
Type an Arabic number or a Roman numeral: the calculator works out the direction by itself, shows the conversion and the breakdown into symbols, and flags non-standard forms such as IIII.
How Roman numerals are written
Roman numerals use seven letters: I = 1, V = 5, X = 10, L = 50, C = 100, D = 500 and M = 1000. The values add up from left to right, largest to smallest: MDCLXVI = 1000 + 500 + 100 + 50 + 10 + 5 + 1 = 1666.
The subtractive rule avoids four equal symbols in a row: a smaller symbol placed before a larger one is subtracted. Only six pairs are allowed: IV = 4, IX = 9, XL = 40, XC = 90, CD = 400 and CM = 900. So 1994 becomes M + CM + XC + IV = MCMXCIV, and 2025 is MMXXV.
These rules reach 3999, MMMCMXCIX. For larger numbers the Romans drew a bar over the letters, multiplying their value by a thousand: V̅ is 5000 and X̅ 10,000. The form IIII, seen on many clock faces, is historical but not the standard one.
Common mistakes
- Subtracting any symbol: 99 is not IC but XCIX, because I is only subtracted from V and X.
- Repeating V, L or D: VV is not used, it is written X.
- Writing more than three equal symbols in a row, as XXXX instead of XL.
Frequently asked questions
Is there a zero in Roman numerals?
No: the Romans had no symbol for zero. In the Middle Ages some texts used the word nulla or the letter N, but it was not part of the numeral system.
Why do clocks show IIII instead of IV?
It is a clockmakers' tradition: IIII visually balances the VIII on the other side of the dial. Both read as 4, but the standard form is IV.
How is the year 2025 written in Roman numerals?
MMXXV: M twice (2000), X twice (20) and V (5).
How this calculation works
Arabic to Roman: repeatedly subtract the largest value from 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, I 1 and write its symbol. Above 3999 the thousands are converted the same way and written with a bar over them. Roman to Arabic: read left to right, adding each value, or subtracting it when the next symbol is larger; the result is converted back to check that the form is the standard one.