Roman Numeral Converter

How to Use This Converter

Type a number in the decimal box to see its Roman numeral equivalent. Or type a Roman numeral in the other box to convert it back to a regular number. The converter works in both directions instantly. Numbers from 1 to 3999 are supported, which covers the standard Roman numeral range.

The Seven Roman Numeral Symbols

Subtractive Notation

Normally, symbols are written largest to smallest and added together. VIII = 5 + 1 + 1 + 1 = 8. But when a smaller symbol comes before a larger one, you subtract it instead. This is called subtractive notation.

There are exactly six subtractive pairs to learn: IV = 4, IX = 9, XL = 40, XC = 90, CD = 400, CM = 900. Any other combination simply adds. So XIV = 10 + (5 - 1) = 14.

How to Convert Step by Step

Use the greedy approach. Start with the largest symbol value that fits, write it down, subtract it from your number, then repeat. To convert 1999:

1. 1999 - 1000 = 999. Write M.
2. 999 - 900 = 99. Write CM.
3. 99 - 90 = 9. Write XC.
4. 9 - 9 = 0. Write IX.

Result: MCMXCIX. Keep going until you reach 0.

Where Roman Numerals Appear Today

• Clock and watch faces (especially analog clocks)
• Super Bowl numbering (Super Bowl LVIII, etc.)
• Movie release years in credits
• Chapter headings in books
• Monarch names like King Charles III

Common Mistakes to Avoid

• Writing IIII instead of IV. The correct way to write 4 is IV.
• Putting a smaller symbol before a larger one when it is not one of the six valid subtractive pairs.
• Using the same symbol more than three times in a row. You can write III but not IIII or XXXX.
• Trying to write 0 or numbers above 3999 in standard Roman numerals. The system does not cover those.