Roman Numerals to Numbers, Both Ways
Type a whole number from 1 to 3999, or a numeral like MCCXXXIV. The other box answers as you type.
1234MCCXXXIV
How Roman Numerals Are Built
Seven letters carry the whole system: I is 1, V is 5, X is 10, L is 50, C is 100, D is 500 and M is 1000. Read left to right, largest values first, adding as you go. When a smaller letter sits before a larger one, subtract it instead: IV is 4, IX is 9, XL is 40, XC is 90, CD is 400, CM is 900.
Only six subtractive pairs exist
Those six are the complete list. VX is not 5, IC is not 99, and IIII is not 4 in standard notation, even though old clock faces stubbornly disagree. This converter rejects all of them and tells you why under the boxes.
Why it stops at 3999
Standard notation repeats a letter at most three times and has no symbol above M. That caps the system at MMMCMXCIX, or 3999. The Romans wrote larger figures with an overline multiplying by 1000, a mark plain text can't reproduce, so 3999 is where this page draws the line.
Reading long numerals
Break them at each value drop. MCCXXXIV splits into M, CC, XXX, IV: 1000 + 200 + 30 + 4 = 1234. Practice on movie credits, they hide production numbers in exactly this form.