Roman Numeral Converter
Convert numbers into Roman numerals and decode Roman numerals back into standard numbers.
Converted Output
Subtractive notation and its rules
Roman numerals use seven symbols — I, V, X, L, C, D, M for 1, 5, 10, 50, 100, 500, 1000 — and are read by adding values left to right. The exception is subtractive notation: a smaller value placed before a larger one is subtracted, so IV is 4 and IX is 9 rather than writing IIII and VIIII.
The subtraction is constrained rather than free-form. Only I, X and C can be subtracted, and each only from the next two higher symbols: I from V and X, X from L and C, C from D and M. That makes IV, IX, XL, XC, CD and CM the complete set of valid subtractive pairs — IL for 49 is invalid, and the correct form is XLIX. Symbols also never repeat more than three times consecutively, which is why the subtractive forms exist at all.
The system has no zero and no straightforward way to express fractions or very large numbers, which is a large part of why positional decimal notation displaced it for calculation. A bar over a numeral multiplied it by a thousand in later usage. It survives in clock faces, book prefaces, monarch regnal numbers, and film copyright dates.
Frequently asked questions
How to convert numbers to Roman Numerals?
Roman numerals use letters I (1), V (5), X (10), L (50), C (100), D (500), and M (1000) to represent values.
What are the rules for writing Roman numerals?
Symbols are I=1, V=5, X=10, L=50, C=100, D=500, M=1000, written largest to smallest and added. Subtractive pairs handle the exceptions: IV=4, IX=9, XL=40, XC=90, CD=400, CM=900. Only I, X and C are used subtractively, and only before the next two larger symbols.
Why is the largest Roman numeral 3,999?
Because standard notation has no symbol above M and allows at most three repetitions, capping the total at MMMCMXCIX. Larger values historically used a vinculum - a bar over a numeral multiplying it by 1,000 - but that convention is not part of standard modern usage.
Is there a Roman numeral for zero?
No. The system was built for counting and commerce and had no positional notation, so it never needed a placeholder. Medieval scholars occasionally wrote the Latin nulla for nothing, but it was not a numeral. The absence of zero is one reason Roman numerals are hopeless for arithmetic.