Roman Numeral Converter

The Roman Numeral Converter translates whole numbers between 1 and 3999 into Roman numerals and parses Roman numerals back into integers, entirely in your browser. Roman numeral notation still shows up in copyright years, clock faces, outline numbering, monarch and Super Bowl naming, and the occasional legacy data field — this tool handles both directions instantly as you type.

Integer-to-Roman conversion uses the standard subtractive notation (IV instead of IIII, IX instead of VIIII) by greedily matching the largest value-symbol pairs, including the six subtractive combinations (CM, CD, XC, XL, IX, IV). Roman-to-integer parsing is strict: rather than naively summing symbol values, it parses the numeral, converts the resulting integer back to its canonical Roman form, and checks that the two match. This catches malformed input a naive parser would silently accept — "IIII" (should be "IV"), "VX" (not a valid subtractive pair), or "IC" — and reports a clear error instead of a wrong answer.

Standard notation has no symbol for zero and no clean way to represent negatives or values ≥ 4000, so this tool intentionally rejects input outside the 1–3999 range. A static reference table of the seven base symbols (I, V, X, L, C, D, M) is shown below the converter for quick lookup.