Roman Numeral Converter

Convert any number from 1 to 3999 into Roman numerals, or decode a Roman numeral back into a number — both directions update live.

Number (1–3999)

Roman numeral

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How it works

Roman numerals are built from seven letters — I, V, X, L, C, D, and M — worth 1, 5, 10, 50, 100, 500, and 1000. The clever part is subtractive notation: a smaller value placed before a larger one is subtracted, so IV means 4 instead of IIII, and CM means 900. To encode a number, the converter repeatedly subtracts the largest fitting Roman value (greedy algorithm) until nothing remains; to decode, it reads the numeral right to left, adding each value and subtracting it when it's smaller than the value already seen. Only numbers 1 through 3999 have standard forms, which is why the tool enforces that range, and malformed numerals like IIII or VV are rejected rather than guessed at.