About this tool
This converter turns any number from 1 to 3,999 into its standard Roman numeral and reads a Roman numeral back into a number, updating both directions as you type. It shows how the numeral is assembled (1994 = M + CM + XC + IV) so you can see why the subtractive pairs CM, XC, and IV appear, and it rejects malformed input such as IIII or VX with a specific message rather than guessing. An optional vinculum mode extends the range to 3,999,999 by drawing a bar over the thousands. It is useful for reading dates on buildings, film copyrights, book prefaces, clock faces, Super Bowl and Olympic numbering, and for checking homework. A chart of the years 2000 to 2099 and a reference table of 1 to 20, the tens, hundreds, and thousands are included.
How it works
Number to numeral uses the greedy subtraction algorithm: starting with the largest of the thirteen values M (1000), CM (900), D (500), CD (400), C (100), XC (90), L (50), XL (40), X (10), IX (9), V (5), IV (4), and I (1), subtract it as many times as possible, append its symbol each time, then move to the next smaller value. Numeral to number reads left to right, adding each symbol's value unless it is smaller than the next symbol, in which case it is subtracted. Validity is checked against the strict standard form as a single regular expression, M{0,3}(CM|CD|D?C{0,3})(XC|XL|L?X{0,3})(IX|IV|V?I{0,3}), which forbids four repeats, repeating V, L, or D, and subtracting across more than one step (such as IC for 99). In vinculum mode a combining overline (U+0305) marks symbols multiplied by 1,000.
Frequently asked questions
Why is 4 written IV and not IIII?
Standard modern form uses subtractive notation: a smaller symbol placed before a larger one is subtracted, so IV is 5 - 1 = 4 and IX is 10 - 1 = 9. IIII was common in antiquity and still appears on clock faces for visual balance, but the strict form used by this converter (and by most style guides) allows at most three repeats of I, X, C, or M, and never repeats V, L, or D.
What is the largest number in Roman numerals?
In standard notation the largest is 3,999, written MMMCMXCIX, because M can appear at most three times and there is no single symbol for 5,000. The Romans and later scribes extended the system with a vinculum, a bar drawn over a group of symbols to multiply it by 1,000; with that convention the limit becomes 3,999,999. Turn on the vinculum option to use it.
Is there a Roman numeral for zero?
No. Roman numerals are an additive tally system with no place value, so they never needed a zero symbol. Medieval writers occasionally used the word nulla or the letter N in tables, but it is not part of the numeral system, and this converter accepts only whole numbers from 1 upward.
How do I read a Roman numeral date like MCMXCIV?
Break it into descending groups: M = 1000, CM = 900, XC = 90, IV = 4, giving 1994. The rule is that when a symbol is followed by a larger one, the pair forms a subtraction. This converter prints exactly that breakdown as a table. Film copyright years and building cornerstones commonly use this form; MMXXVI is 2026.