Roman Numeral Converter

What are Roman numerals?

Roman numerals are a numeral system originating in ancient Rome that uses combinations of letters from the Latin alphabet to represent values: I (1), V (5), X (10), L (50), C (100), D (500), and M (1000). Despite being over 2,000 years old, Roman numerals remain widely used today for clock faces, chapter numbering, movie sequel titles, Super Bowl editions, and formal documents.

The system works by addition and subtraction. Symbols are generally written from largest to smallest, left to right, and their values are added. When a smaller symbol appears immediately before a larger one, it is subtracted instead. This subtractive principle is how 4 (IV), 9 (IX), 40 (XL), 90 (XC), 400 (CD), and 900 (CM) are written.

Roman numeral symbols

The seven basic symbols are: I = 1, V = 5, X = 10, L = 50, C = 100, D = 500, M = 1000. Only I, X, C, and M can be repeated (up to three times in succession). The subtractive pairs are: IV (4), IX (9), XL (40), XC (90), CD (400), CM (900).

Conversion rules

To convert a decimal number to Roman numerals, break it into thousands, hundreds, tens, and ones, then write each component using the appropriate symbols. For example, 1994 = 1000 + 900 + 90 + 4 = M + CM + XC + IV = MCMXCIV. To convert Roman numerals to decimal, read left to right, adding each symbol's value unless a smaller symbol precedes a larger one, in which case subtract it.

How to use this tool

Enter a decimal number (1–3999) or a Roman numeral string. The tool converts in both directions automatically. Invalid inputs are detected and reported with specific error messages.

Range limitations

Standard Roman numerals can represent numbers from 1 to 3,999 (MMMCMXCIX). There is no symbol for zero — the Romans had no concept of zero as a number. For values above 3,999, medieval scribes used a horizontal bar (vinculum) over a symbol to multiply it by 1,000, but this notation is rarely used today.

Common Roman numerals in everyday life

• Years: 2024 = MMXXIV, commonly seen on building cornerstones and movie credits.
• Events: Super Bowl LVIII = 58, Olympics editions.
• Books and documents: Chapter XII, Volume III, Appendix IV.
• Clocks: Many clock faces use Roman numerals, often writing 4 as IIII instead of IV.

Frequently asked questions

Why do clocks use IIII instead of IV?

This is a long-standing tradition with several theories. The most common explanation is visual balance — IIII on the left side of the clock balances VIII on the right. Another theory is that IV was the abbreviation for Jupiter (IVPITER) in ancient Rome, and using it on a clock was considered disrespectful.

Did the Romans use Roman numerals for arithmetic?

Not exactly. Romans performed calculations using an abacus (counting board) and only recorded the results in Roman numerals. The numeral system itself is poorly suited for arithmetic — try multiplying MCMXCIV by XVII without converting to decimal first. This is one reason why Arabic numerals eventually replaced Roman numerals for mathematics.