Roman Numeral Converter
Convert between Roman numerals and standard numbers.
Roman numerals appear in clock faces, book chapters, movie sequels, building cornerstones, and formal documents, but converting between Roman and Arabic numerals by hand is error-prone. This converter handles both directions instantly, validating the input and supporting values up to 3,999.
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How to Convert Roman Numerals
- Enter a number or Roman numeral — type a decimal number (1–3999) or a Roman numeral string (e.g., MCMXCIV).
- Click Convert — the tool instantly converts between the two formats.
- Review the result — see the full breakdown and verify with the reference chart below.
- Learn the patterns — study how subtractive notation works (IV = 4, IX = 9, XL = 40, etc.).
Frequently Asked Questions
How do Roman numerals work? ▼
Roman numerals use seven symbols: I (1), V (5), X (10), L (50), C (100), D (500), M (1000). Letters are combined additively (VIII = 8) and subtractively (IV = 4, IX = 9). The subtractive rule: a smaller numeral before a larger one means subtract (e.g., XL = 40, CD = 400).
What is the largest number in Roman numerals? ▼
Standard Roman numerals go up to 3,999 (MMMCMXCIX). Numbers beyond this traditionally use a vinculum (overline) to multiply by 1,000 — for example, V̅ = 5,000. In modern usage, large numbers are typically written in Arabic numerals.
Why do clocks use IIII instead of IV? ▼
Many clock faces display 4 as IIII rather than IV. The most popular theory is aesthetic balance — IIII creates visual symmetry with VIII on the opposite side. Some historians also suggest it avoids confusion with IV (the first letters of IVPITER/Jupiter in Latin).
Where are Roman numerals still used today? ▼
Roman numerals appear in clock faces, movie copyright dates, Super Bowl numbering, book chapter numbers, monarch names (Elizabeth II), chemistry (Group IV elements), music (IV chord), outlines, and building cornerstones. They remain a widely recognised numbering system.
What is subtractive notation in Roman numerals? ▼
Subtractive notation places a smaller numeral before a larger one to indicate subtraction: IV = 4 (5−1), IX = 9 (10−1), XL = 40 (50−10), XC = 90 (100−10), CD = 400 (500−100), CM = 900 (1000−100). Only I, X, and C can be used subtractively.
Is my data stored? ▼
No. The conversion happens entirely in your browser. No data is sent to any server.