Roman numeral converter
Roman numerals use seven letters and a subtractive rule: a smaller symbol before a larger one is subtracted, so IV is 4 and CM is 900. This converts both ways and rejects malformed numerals such as IIII or IC rather than guessing.
- Number
- 2,026
- Symbols used
- 6
- How it is built
- MM (2000) + XX (20) + V (5) + I (1)
The formula
Values: I 1, V 5, X 10, L 50, C 100, D 500, M 1000. Subtractive pairs: IV 4, IX 9, XL 40, XC 90, CD 400, CM 900. A number is written by taking the largest value that fits, repeatedly. A numeral is valid only if writing its value back produces exactly the same letters.
Worked example
2026 is MMXXVI: MM for 2000, XX for 20, VI for 6. MCMXCIV is 1994: M 1000, CM 900, XC 90, IV 4.
How to use it
- 1The range is 1 to 3999. Larger numbers needed a bar over the symbol, which has no standard plain-text form.
- 2There is no zero and no negative numbers in the Roman system.
- 3Lower-case input is accepted and read as upper case.
Questions people ask
Why is IIII rejected when clocks use it?
Clock faces use IIII by long tradition, for visual balance against VIII. In standard notation the form is IV, and the strict check accepts only the form that the rules produce.
How do I write a year in Roman numerals?
Exactly like any other number: 1999 is MCMXCIX, 2000 is MM. The year is written as one whole number, not split into parts.
Last reviewed: 2026-10-20