Roman Numeral Converter
Convert numbers to Roman numerals and Roman numerals back to numbers, live as you type, for any value from 1 to 3999.
🔒 Processed locally in your browser
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How to use
- Choose a direction using the toggle: Number → Roman or Roman → Number.
- Type a whole number from 1 to 3999, or a Roman numeral like MCMXCIV, into the input field.
- The converted result appears instantly below — there's no button to press.
- Use the Copy button to copy the result, or Reset to clear the field and start over.
Features
- Converts both ways: numbers to Roman numerals and Roman numerals to numbers
- Updates live as you type — no button to press
- Supports the full traditional range from 1 to 3999
- Strictly validates Roman numeral input and rejects malformed forms like "IIII" or "VV"
- 100% client-side — your input never leaves your browser
Frequently asked questions
What is the valid range for this converter?
1 to 3999. Traditional Roman numerals have no standard symbol for zero or for 4000 and above, so numbers outside this range can't be represented without non-standard notation (such as a bar over a numeral to mean "times 1000"), which this tool doesn't use.
How does number-to-Roman conversion work?
It uses the classic greedy algorithm: starting from the largest value (1000, then the subtractive pairs like 900, 500, 400, and so on down to 1), it repeatedly subtracts the largest symbol that still fits, appending its letters, until nothing remains.
Why is "IIII" rejected instead of being read as 4?
Standard Roman numeral form always uses subtractive notation for 4 and 9 within each order of magnitude (IV, IX, XL, XC, CD, CM), and never repeats a symbol more than three times in a row. "IIII" and similar forms aren't standard, so this tool flags them as invalid rather than guessing what you meant.
Is Roman numeral input case-sensitive?
No. You can type in uppercase, lowercase, or a mix (e.g. "mcmxciv") and it will be converted the same as "MCMXCIV".
Does this tool store or upload what I type?
No. All conversion happens locally in your browser using JavaScript. Nothing you enter is sent to a server or saved anywhere.