Convert numbers to Roman numerals and back — live, both ways. Type in either field and the other updates instantly. Strict validation rejects malformed numerals, and large values use vinculum (overline) notation up to 3,999,999. Everything runs entirely in your browser.
Standard Roman numerals cover 1–3999. For larger values (up to 3,999,999) an overline multiplies a numeral by 1,000 — shown here as a bar over the letters, e.g. IV = 4,000.
Enter letters I, V, X, L, C, D, M. Malformed numerals such as IIII or VX are rejected.
Subtractive pairs: IV=4, IX=9, XL=40, XC=90, CD=400, CM=900. A letter never repeats more than three times in a row, and V, L, D never repeat.