Convert integers 1–3999 to Roman numerals, or parse common Roman strings back to Arabic.
Arabic → Roman uses subtractive pairs (IV, IX, XL, XC, CD, CM) for 1–3999. Roman → Arabic uppercases, strips characters outside MDCLXVI, then applies a simple left‑to‑right rule (subtract if a token is smaller than the next). Malformed input may still yield a number—large or odd results should be double‑checked.
This calculator uses plain decimal numbers. If a result looks wrong, check whether you used a comma instead of a dot (or vice versa) where the field expects one.