Roman Numeral Converter

What Is a Roman Numeral Converter?

The Roman numeral converter translates between the ancient numbering system used by the Romans and the Arabic (Hindu-Arabic) numerals we use today. Roman numerals are still widely used for clock faces, book chapters, film sequels, sporting events (Super Bowl), and formal inscriptions on buildings. Understanding how to read and write them is both a practical skill and a connection to mathematical history.

Roman numerals use seven symbols: I (1), V (5), X (10), L (50), C (100), D (500), and M (1000). The system is primarily additive — symbols are placed from largest to smallest and their values are summed. However, a subtractive rule applies when a smaller symbol precedes a larger one: IV = 4, IX = 9, XL = 40, XC = 90, CD = 400, and CM = 900. This prevents four consecutive identical symbols (IIII is written as IV).

The standard Roman numeral system represents numbers from 1 to 3,999. There is no symbol for zero, and numbers above 3,999 historically used overline notation (a bar above a symbol to multiply by 1,000). This converter handles the standard range and shows the additive and subtractive breakdown for each conversion, making it a useful educational tool for understanding the structure of the system.

How Do You Use This Roman Numeral Converter?

Enter a Roman numeral (e.g., MCMXCIV) or a standard number (e.g., 1994) and click Convert. The calculator detects which format you entered and converts to the other, showing the breakdown of each symbol.

1. Enter a Roman numeral (letters like XIV) or a standard number (digits like 14) in the input field.
2. Click Convert — the calculator auto-detects the input format.
3. Read the converted value in the results panel.
4. Review the breakdown showing how each Roman numeral group maps to a value.
5. For Roman-to-number conversions, check each subtractive pair (IV, IX, XL, etc.).
6. For number-to-Roman conversions, verify the largest-to-smallest symbol order.

How Does the Roman Numeral Converter Formula Work?

The formula used: Additive: VI = 5+1 = 6. Subtractive: IV = 5−1 = 4. Symbols: I=1, V=5, X=10, L=50, C=100, D=500, M=1000

What Are Some Example Calculations?

MCMXCIV → M=1000, CM=900, XC=90, IV=4 → 1994. Conversely, 2024 → MM=2000, XXIV=24 → MMXXIV.

When Should You Use a Roman Numeral Converter?

Use this converter whenever you encounter Roman numerals and need the standard number, or when you need to write a number in Roman numeral form. Common situations include reading dates on buildings and monuments, numbering chapters or sections in formal documents, understanding film or event numbering (e.g., Super Bowl LVIII), and working with clock faces.

Students and educators find it useful for learning the Roman numeral system. Writers and publishers use it for front matter pagination (i, ii, iii, iv) and chapter headings. Historians and classicists encounter Roman numerals in primary sources. The converter also helps when creating formal invitations, legal documents, or academic papers that use Roman numeral numbering conventions.

What Do These Terms Mean?

What Are the Best Tips to Know?

• Remember the six subtractive pairs: IV (4), IX (9), XL (40), XC (90), CD (400), CM (900) — they are the only valid subtractive combinations.
• A symbol can repeat up to three times (III, XXX, CCC, MMM) but never four — use the subtractive form instead.
• V, L, and D are never subtracted and never repeated — they appear only once in their respective decimal place.
• Read Roman numerals left to right, watching for subtractive pairs where a smaller symbol precedes a larger one.
• The maximum standard Roman numeral is MMMCMXCIX (3,999). For larger numbers, historical texts used overline notation.

What Mistakes Should You Avoid?

• Writing IIII instead of IV, or XXXX instead of XL — while IIII appears on some clock faces, the standard form uses subtractive notation.
• Using invalid subtractive pairs like IC (should be XCIX for 99) or VX (V is never subtracted).
• Placing symbols in the wrong order — Roman numerals must go from largest to smallest value, left to right.
• Assuming there is a Roman numeral for zero — the Roman system has no symbol for zero.