Free Online Roman Numeral Converter
Convert any whole number from 1 to 3999 into its Roman numeral equivalent, or convert a Roman numeral string back to an Arabic number. Invalid numerals are detected and rejected.
Roman Numeral Symbol Reference
| Symbol | Value |
|---|---|
| I | 1 |
| V | 5 |
| X | 10 |
| L | 50 |
| C | 100 |
| D | 500 |
| M | 1000 |
Subtractive notation: placing a smaller symbol before a larger one means subtraction — IV = 4, IX = 9, XL = 40, XC = 90, CD = 400, CM = 900.
Frequently Asked Questions
Standard Roman numeral notation has no symbol for values of 5000 or more, so 3999 (MMMCMXCIX) is the largest number representable with the standard I, V, X, L, C, D, M symbols alone. Larger numbers historically used a bar over a symbol to multiply it by 1000, which isn't part of everyday Roman numeral usage.
When a smaller-value symbol appears immediately before a larger one, it's subtracted rather than added: IV = 5 − 1 = 4, IX = 10 − 1 = 9, XL = 50 − 10 = 40. Only specific pairs are valid (I before V/X, X before L/C, C before D/M) — that's what this tool's validation checks for.
No — the Romans had no symbol or concept for zero as a numeral in this system, which is why this converter (and Roman numerals generally) starts at 1.
Yes, it validates the input and rejects strings that don't follow proper Roman numeral rules — like repeating a subtractive pair or stacking too many of the same symbol — rather than silently guessing at a value.
It's completely free with no limits, and nothing is sent anywhere — conversion happens entirely in your browser using JavaScript.