Roman Numeral Converter
This free Roman numeral converter works in both directions: type a number to see it as a Roman numeral, or type a Roman numeral to see it as a number. The direction is detected automatically from what you type. Nothing you enter is sent anywhere or stored.
How to Use It
- Type a whole number (1 to 3999) to convert it to a Roman numeral.
- Or type a Roman numeral (using I, V, X, L, C, D, M) to convert it to a number.
- The result updates instantly as you type, no submit button.
How It Works
Roman numerals use seven symbols, each with a fixed value: I is 1, V is 5, X is 10, L is 50, C is 100, D is 500, and M is 1,000. Normally symbols are written largest to smallest and their values added together, but when a smaller symbol appears immediately before a larger one, its value is subtracted instead. That subtractive notation is what turns 4 into "IV" (5 minus 1) rather than "IIII" (four 1s in a row), and is limited to six specific pairs: IV, IX, XL, XC, CD, and CM.
Formula
number to Roman: repeatedly subtract the largest matching value (M, CM, D, CD, C, XC, L, XL, X, IX, V, IV, I) and append its symbol, until nothing remains
A worked example: 1994 breaks down as 1000 (M) + 900 (CM) + 90 (XC) + 4 (IV), giving MCMXCIV. Converting back, MCMXCIV reads as M (1000) + CM (900) + XC (90) + IV (4), adding back up to 1994. The current year, 2026, converts to MMXXVI (1000 + 1000 + 10 + 10 + 5 + 1).
Everything runs client-side in your browser. Nothing you enter is sent anywhere or stored.
Frequently Asked Questions
Why is the range limited to 1 through 3999?
Standard Roman numerals have no symbol for zero or negative numbers, and there is no standard single-character notation above 3999 (repeating M a fourth time is not valid, and the historical overline convention for larger numbers is not practical in plain text). This 1 to 3999 range is the conventional limit essentially every Roman numeral converter uses.
Why does entering something like "IIII" or "VX" produce an error instead of a number?
Both are not standard Roman numerals. The number 4 is written "IV" (one less than five), not "IIII", and "VX" is not a valid combination under the standard subtractive notation rules at all. This tool validates against well formed Roman numerals rather than loosely guessing at what a malformed one might have meant.
How does the tool know whether I want a number or a Roman numeral?
It looks at what you typed. Digits convert to a Roman numeral, and letters (I, V, X, L, C, D, M) convert to a number, so there is nothing to select first, just type either one into the same field.
What is the subtractive notation rule?
Normally, symbols are added together from left to right (VI is 5 plus 1, or 6). When a smaller symbol appears immediately before a larger one, it is subtracted instead (IV is 5 minus 1, or 4). Only specific pairs are standard: IV, IX, XL, XC, CD, and CM, which is why this tool rejects other combinations like "IIX" or "VX".
Where are Roman numerals actually still used today?
Common places include copyright years and sequel numbering in film credits, clock and watch faces, chapter or section numbers in books, the naming of monarchs and Super Bowls, and outlines. Birth years, anniversaries, and tattoos are also common personal uses, since a year like 1994 written as MCMXCIV reads as a single meaningful symbol rather than four separate digits.