Roman Numeral Converter

Convert Roman numerals

The Roman numeral converter changes Arabic numbers into Roman numerals and back again. The valid range is 1 to 3999. The system uses seven basic symbols: I (1), V (5), X (10), L (50), C (100), D (500) and M (1000). The distinctive feature is the subtractive notation, where a smaller value placed before a larger one is subtracted from it.

How it works

The subtractive notation follows fixed rules: I precedes V or X (IV = 4, IX = 9), X precedes L or C (XL = 40, XC = 90), and C precedes D or M (CD = 400, CM = 900). These rules prevent any symbol from being repeated more than three times in a row. Take 1994: it breaks down into 1000 (M), then 900 (CM, that is 1000 minus 100), then 90 (XC, that is 100 minus 10), and finally 4 (IV, that is 5 minus 1). Together they give MCMXCIV.

Another example: 2024 becomes MMXXIV, because 1000 + 1000 + 10 + 10 + 5 minus 1 yields this year number. Conversion works in both directions: the converter reads a Roman input from left to right, adding or subtracting depending on the arrangement of symbols.

What the tool can and cannot do

The converter correctly handles all numbers from 1 to 3999 in both directions. It automatically detects whether you are entering a Roman or an Arabic number and immediately shows the counterpart. However, the system has no zero value because the Romans did not use one. Decimal fractions or values above 3999 fall outside the valid range and cannot be represented.

Why local processing in the browser

The calculation runs entirely on your device. Your input never leaves the computer; there is no server receiving or storing data. You can use the converter offline once the page is loaded, and try it as many times as you like without anything being logged. This also means there is no attack surface and your data is not transmitted over the network.

Frequently asked questions