Roman Numeral Converter - Arabic ↔ Roman Numerals

How to use this tool

1. Choose a direction. Select "Arabic → Roman" to convert a number to Roman numerals, or "Roman → Arabic" to convert Roman numerals to a number.
2. Enter your value. Type an Arabic number (1–3,999,999) or a Roman numeral using I, V, X, L, C, D, M. For large Roman values, paste the combining-overline form or use an ASCII alias such as _V; aliases can prefix each overlined letter.
3. Read the result. The converted value appears instantly. Copy it to your clipboard with the Copy button.

How Roman numerals work

Roman numerals use seven letters: I (1), V (5), X (10), L (50), C (100), D (500), and M (1,000). Numerals are generally written from largest to smallest, left to right, and values are added together. The special cases are the six subtractive pairs:

• IV = 4 (5 − 1)
• IX = 9 (10 − 1)
• XL = 40 (50 − 10)
• XC = 90 (100 − 10)
• CD = 400 (500 − 100)
• CM = 900 (1,000 − 100)

Roman numerals reference table 1–20

Roman numerals reference table for hundreds and thousands

Common uses of Roman numerals today

Roman numerals are still widely used for: clock faces (I–XII), chapter and book numbering, movie sequel numbering (e.g., Rocky IV), Super Bowl numbering, Olympic Games years, copyright years on film and TV credits, and formal outlines.

Why do clock faces show IIII instead of IV?

Many clock faces use IIII instead of IV. Theories include: aesthetic balance (four I's mirror the VIII on the opposite side), avoiding confusion with the Roman numeral for "Jupiter" (IV was an abbreviation), and a historical preference by clockmakers. This converter uses standard academic notation (IV for 4).

Medieval and modern extensions

Standard Roman numeral notation tops out at 3,999 (MMMCMXCIX). This converter also supports vinculum overline forms up to 3,999,999: a bar multiplies the marked letter’s value by 1,000. When entering a large Roman numeral, use its combining-overline form or an ASCII alias such as _V for V̄. The decoder accepts both the combining macron and combining overline marks.

• V̄ = 5,000
• X̄ = 10,000
• L̄ = 50,000
• C̄ = 100,000
• D̄ = 500,000
• M̄ = 1,000,000

The encoder uses the standard subtractive forms for values through 3,999, then adds overlined tokens for larger place values. For example, V̄ represents 5,000, and this converter supports the same notation in both directions through 3,999,999.

Year conversion reference