Roman Numeral Converter
Convert numbers to Roman numerals and back — free, instant, no signup
Processed locally in your browserRoman numeral appears here
Batch Conversion
Enter one value per line. Using the direction selected above (Number → Roman).
Results will appear here...
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How to Use
Convert any integer (1–3999) to Roman numerals, or decode a Roman numeral string back to a number, entirely in your browser.
- Select your conversion direction: click "Number → Roman" or "Roman → Number" using the toggle at the top.
- Type a number (1–3999) or a Roman numeral string into the input field — the result appears instantly.
- Review the step-by-step breakdown below the output to understand how the conversion was derived.
- Click the Copy button to copy the result to your clipboard with one click.
- Use the Batch Conversion section at the bottom to convert multiple values at once — paste one value per line.
Features
- ✓Bidirectional conversion: integer to Roman numeral and Roman numeral to integer
- ✓Instant live conversion as you type
- ✓Step-by-step breakdown showing how each conversion is built
- ✓Validation with clear error messages for invalid input
- ✓Collapsible reference chart with all symbols and subtractive pairs
- ✓Batch conversion for multiple values at once (one per line)
- ✓Supports the full standard range of 1–3999
- ✓Copy result to clipboard with one click
- ✓Dark mode support and full keyboard accessibility
Frequently Asked Questions
- What is the valid range for Roman numeral conversion?
- Standard Roman numerals cover the range 1 to 3999 (I to MMMCMXCIX). Numbers outside this range cannot be represented using the classical subtractive notation system.
- How does Roman numeral subtraction work?
- When a smaller value symbol appears immediately before a larger value symbol, it is subtracted rather than added. The valid subtractive pairs are IV (4), IX (9), XL (40), XC (90), CD (400), and CM (900). All other combinations are additive.
- Are Roman numerals case-sensitive?
- No. Both uppercase (XIV) and lowercase (xiv) are accepted as input. The converter normalises all input to uppercase before processing.
- Why does the converter reject certain Roman numeral sequences?
- Invalid sequences such as "IIII", "VV", or "IIX" are rejected because they violate standard notation rules. The same symbol may appear at most three times consecutively, and only specific subtractive pairs are permitted.
- What is the history behind Roman numerals?
- Roman numerals originated in ancient Rome around 900–800 BC and were used throughout the Roman Empire for counting and record-keeping. Derived from tally marks, the system uses letters I, V, X, L, C, D, and M. Although largely replaced by the Hindu-Arabic numeral system in the Middle Ages, Roman numerals are still used today for clock faces, film copyright dates, book chapters, and formal document numbering.