Roman numeral converter

How to use the Roman numeral converter

1. Choose a direction: number to Roman numeral, or Roman numeral to number.
2. Enter a number between 1 and 3999, or a valid Roman numeral.
3. The result appears instantly as you type.
4. Toggle the reference table to see the Roman numeral symbols and their values.

Common uses

• Reading clock faces: analog clocks often use Roman numerals for their hour markers
• Film credits and cornerstones: convert a year such as MCMXCIV to 1994, then count the years since that date
• Outlines and chapter numbers, with the math tools guide covering the notation rules; for binary, octal or hex, switch number bases instead

Technical specification

• Algorithm or formula: Greedy decimal-to-Roman conversion using the 13 symbol-value pairs M (1000), CM (900), D (500), CD (400), C (100), XC (90), L (50), XL (40), X (10), IX (9), V (5), IV (4), I (1). Roman-to-decimal matches the same 13 symbols from left to right, adds their values, then writes the total back as a numeral. Input that does not round-trip, such as IIII, IC or VX, is reported as non-standard, and the standard form is suggested where one exists (IIII becomes IV). The 13 values follow the modern standard form; for the history of the notation, including older forms such as IIII, see Florian Cajori, A History of Mathematical Notations, Vol. 1 (Open Court, 1928).
• Browser API or library: Pure JavaScript; no external library.
• Input limits: Integers 1 to 3,999 (the classical Roman range). Roman input may use only I, V, X, L, C, D and M, in upper or lower case (xiv is read as XIV).
• Output: Roman numeral string or decimal integer, with validation messages for out-of-range or malformed input.
• Known limitations: Numbers above 3,999 (which historically used overbars to indicate multiplication by 1,000) are not supported. Zero and negative numbers have no Roman representation.

Frequently asked questions

What numbers can be converted to Roman numerals?

The standard Roman numeral system covers integers from 1 to 3,999 (MMMCMXCIX). Numbers outside this range cannot be represented using the classical rules. This tool supports the full 1 to 3,999 range.

What are the subtractive rules in Roman numerals?

Roman numerals use subtractive notation for six combinations: IV (4), IX (9), XL (40), XC (90), CD (400), and CM (900). A smaller value placed before a larger one means the smaller is subtracted. All other symbols are additive.

Is this tool completely free?

Yes. The tool is completely free to use with no registration, no account, and no payment required.

Is my data sent to a server?

All conversions run locally in JavaScript in your browser. Our servers are not involved at any point.