Roman Numerals

What are Roman numerals?

Roman numerals are a numeral system originating in ancient Rome, using seven symbols: I (1), V (5), X (10), L (50), C (100), D (500), and M (1000). Numbers are written largest-first, with subtractive notation for values one place below a larger symbol: IV (4), IX (9), XL (40), XC (90), CD (400), CM (900).

They are still used on clock faces, in book and film titles, in outlines, and to number chapters. The largest value conventionally expressible in standard notation is 3,999 (MMMCMXCIX).

How to use

Type a Roman numeral or a decimal number. The tool detects which format you entered and converts to the other. Input is case-insensitive.

For example, MMXXV converts to 2025, and 2025 converts to MMXXV.

Notation rules

The standard subtractive pairs are IV, IX, XL, XC, CD, and CM. Other combinations like IC (99) or VX (5) are not valid in classical use. The tool accepts some non-standard forms on input, such as IIII for 4, but always outputs canonical Roman numerals.

Historically, a bar over a numeral multiplied it by 1,000. This is not supported here because it requires non-ASCII characters and is rarely used today.

FAQ

What is the largest number I can convert?

3,999 in standard notation. Above that, you would need the vinculum (bar) notation, which this tool does not support.

Is IIII a valid Roman numeral?

On clock faces, IIII is often used instead of IV for visual symmetry with VIII. In standard Roman notation, IV is correct. The tool accepts IIII as input but outputs IV.

Are lowercase Roman numerals valid?

They are used in some contexts, such as page numbers in the front matter of books. The tool accepts lowercase and outputs uppercase.

Where are Roman numerals used today?

Clock faces, regnal names (Elizabeth II), sports events (Super Bowl LVIII), film copyright dates, book chapters, and prequel numbering in media franchises.