Roman Numeral Converter
Convert between Roman numerals (XIV, MMXXIV) and regular numbers (1–3999).
Roman Numeral Reference Table
The 13 fundamental Roman numeral symbols and their values.
| Roman | Value | Notes |
|---|---|---|
| I | 1 | Basic unit |
| IV | 4 | Subtractive form (5−1) |
| V | 5 | Half of X |
| IX | 9 | Subtractive form (10−1) |
| X | 10 | Ten |
| XL | 40 | Subtractive form (50−10) |
| L | 50 | Fifty |
| XC | 90 | Subtractive form (100−10) |
| C | 100 | Centum (hundred) |
| CD | 400 | Subtractive form (500−100) |
| D | 500 | Five hundred |
| CM | 900 | Subtractive form (1000−100) |
| M | 1000 | Mille (thousand) |
What Is a Roman Numeral Converter?
A Roman numeral converter translates between the ancient Roman numbering system and modern Arabic numerals. Roman numerals use letters from the Latin alphabet — I, V, X, L, C, D, M — to represent values. This system was widely used throughout the Roman Empire and continues to appear in clock faces, movie credits, book chapters, copyright years, and Super Bowl titles today.
This tool supports all standard Roman numerals from I (1) to MMMCMXCIX (3999), validates your input in real time, shows a step-by-step breakdown of each conversion, and includes a handy reference table.
How to Use This Tool
Choose a conversion direction using the tabs at the top of the tool, then enter your value:
- Number → Roman: Type any integer between 1 and 3999. The Roman numeral equivalent appears instantly, along with a breakdown showing how each part contributes to the result.
- Roman → Number: Type a Roman numeral (e.g. XIV, MMXXIV). The tool validates the input and displays the corresponding Arabic number with a token-by-token breakdown.
- Quick examples: Click the example chips to auto-fill common values and see conversions immediately.
- Copy result: Use the Copy button to copy the conversion to your clipboard in one click.
The tool detects and reports invalid Roman numeral strings — such as repeated subtractive pairs, illegal sequences, or out-of-range numbers — with a clear error message.
Common Use Cases
Frequently Asked Questions
Why does the converter only go up to 3999?
The standard Roman numeral system uses a maximum of three consecutive identical symbols. The largest expressible number without extended notation (vinculum/overline) is 3999 (MMMCMXCIX). Numbers 4000 and above require a bar over symbols to indicate multiplication by 1000, which is outside the standard scope.
What are subtractive notation rules?
When a smaller value precedes a larger one, it is subtracted. Only specific pairs are valid: IV (4), IX (9), XL (40), XC (90), CD (400), and CM (900). For example, 4 is written as IV, not IIII. A symbol can only be used subtractively once per numeral, and only I, X, and C can be used in subtractive position.
Why is IIII sometimes used instead of IV on clocks?
Many clock faces use IIII instead of IV for aesthetic and historical reasons. It creates visual symmetry on the clock face, and historically IIII was the more common form before standardized subtractive notation became widespread. Both forms are technically valid in different contexts.
How does the tool validate Roman numeral input?
The tool uses a regular expression that matches only correctly formed standard Roman numerals. It checks for proper symbol combinations, prevents illegal repetitions (e.g., VV, LL, DD), and ensures subtractive pairs are used correctly. Invalid sequences trigger a red error message explaining the problem.
Is zero representable in Roman numerals?
No. The Roman numeral system has no symbol for zero, which was a significant limitation compared to the Hindu-Arabic numeral system. The Latin word "nulla" (nothing) was sometimes used conceptually, but zero as a number was introduced to Europe from Indian mathematics in the Middle Ages.
What is the longest Roman numeral in the 1–3999 range?
The number 3888 produces the longest Roman numeral: MMMDCCCLXXXVIII (15 characters). It contains three M's, three C's (as DCC), three X's (as LXX), and three I's (as VIII), making it the most "verbose" value in the standard range.