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Convert between Roman numerals and decimal numbers.
Select either Number to Roman or Roman to Number mode.
Type a decimal number or a Roman numeral string in the input field.
Click Copy to save the converted value to your clipboard.
Roman numerals are a number system from ancient Rome that uses letters to represent values: I is 1, V is 5, X is 10, L is 50, C is 100, D is 500, and M is 1000. This converter turns a regular number into Roman numerals and translates Roman numerals back into a regular number.
Enter a value in either field and the conversion is instant. It handles the subtractive notation correctly, so 4 becomes IV rather than IIII and 9 becomes IX, following the standard rules used today.
You build a number by adding symbols from largest to smallest, so XVI is 10 + 5 + 1 = 16. When a smaller symbol comes before a larger one, you subtract it, which is why IV is 5 minus 1 = 4 and CM is 1000 minus 100 = 900. A symbol is never repeated more than three times in a row, which is exactly why subtractive notation exists.
Only I, X, and C are used as subtractors, and only before the next one or two larger symbols. So 4 is IV, 9 is IX, 40 is XL, 90 is XC, 400 is CD, and 900 is CM. Values like IIII or VX are not valid standard numerals, and the converter produces the correct form instead.
Standard Roman numerals only go up to 3999 (MMMCMXCIX) because there is no single symbol for 5000 or 10000. Larger numbers historically used a bar over a numeral to multiply it by 1000, but that notation is rarely needed, so this tool covers the everyday range of 1 to 3999.
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