Roman Numerals Converter

1. Type a number from 1 to 3999 to get the Roman numeral.
2. Or type a Roman numeral to convert it back to a number.
3. Conversion runs both ways and updates as you type.

The system uses I for 1, V for 5, X for 10, L for 50, C for 100, D for 500 and M for 1000.

Symbols add up when written in descending order: XVI is 10 plus 5 plus 1, or 16.

The subtractive rule applies when a smaller symbol precedes a larger one: IV is 4, IX is 9, XL is 40, CM is 900. Only six combinations are valid — IV, IX, XL, XC, CD and CM.

That means IIII is not the canonical form of 4, even though it appears on clock faces by visual tradition. Conversion here follows the strict form.

With the seven available symbols, the largest representable value is MMMCMXCIX, which is 3999. Going higher would need four Ms in a row, which strict notation does not allow.

The Romans used a bar above a symbol to multiply it by a thousand, but that notation has no consistent representation in plain text, so it is left out.

There is also no symbol for zero or for negative numbers: the system works purely by adding and subtracting fixed values, without the empty-place concept that zero provides.