Roman Numeral Converter
Convert between Roman numerals and decimal numbers - validates malformed Roman numerals rather than guessing at invalid input.
Enter either a Roman numeral or a decimal number - this tool converts it, strictly validating Roman numeral input rather than accepting anything that merely looks close.
Edit either field - the other updates. Supports the standard range 1-3999 using conventional subtractive notation (e.g. IV, IX, XL) - malformed combinations like "IIII" or "VX" are rejected rather than guessed at.
Standard Roman numerals only support values from 1 to 3,999 - this tool clearly reports numbers outside that range instead of producing a nonstandard result.
How Roman Numeral Validation Works
Valid Roman numerals follow specific rules (like never repeating certain symbols more than three times in a row, and subtractive notation only being valid in specific combinations like IV or IX) - this tool checks those rules rather than just summing up symbol values, so it correctly rejects invalid combinations like IIII or VX.
How to Use It
- Enter either a Roman numeral or a decimal number (1-3,999).
- View the converted result - invalid Roman numeral input is flagged with an explanation rather than silently accepted.
Supported Range
Standard Roman numerals represent 1 to 3,999 - there's no standard symbol for zero or negative numbers, and numbers at or above 4,000 require non-standard notation (like a bar over a numeral) that this tool doesn't generate.