Roman Numeral Converter
Convert between Roman numerals and decimal numbers. Supports values from 1 (I) up to 3999 (MMMCMXCIX).
Written by Rahman · Last reviewed
Quick answer
Roman numerals use seven letters: I (1), V (5), X (10), L (50), C (100), D (500), M (1,000), read left to right and added together, except where a smaller letter sits before a larger one and is subtracted instead. That is why 4 is IV and 9 is IX. The standard system runs from 1 to 3,999 (MMMCMXCIX); above that a bar over a letter multiplies it by 1,000, a notation rarely used today.
About the Roman Numeral Converter
Roman numerals use seven letters: I (1), V (5), X (10), L (50), C (100), D (500) and M (1,000), combined according to additive and subtractive rules to represent numbers from 1 to 3,999. They appear on clock faces, book chapters, movie copyrights, monarchs' titles and Super Bowl logos.
This converter goes both ways: enter an integer to see its Roman form, or paste a Roman numeral to find its decimal value. It validates input strictly: repeated symbols like "IIII" or "VV" are flagged as invalid.
The subtractive rule, and where it applies
Roman numerals are mostly additive: symbols are written largest to smallest and summed. The exception is subtraction: a smaller symbol placed before a larger one is subtracted from it, which is why 4 is IV rather than IIII and 9 is IX rather than VIIII.
The rule is narrower than it first appears. Only six subtractive pairs are valid in standard notation: IV, IX, XL, XC, CD and CM. I can precede only V and X, X only L and C, and C only D and M. Combinations such as IL for 49 or IC for 99 are not valid: 49 is XLIX.
- Only powers of ten (I, X and C) are ever subtracted. V, L and D are never used subtractively.
- A symbol may repeat at most three times consecutively, which is why the converter rejects IIII and VIIII.
- V, L and D never repeat at all, since two of any of them would simply be the next symbol up.
Clock faces are the famous exception: many use IIII for four rather than IV, a convention long predating any standardisation and generally explained by visual balance against the VIII opposite it.
No zero, and an upper limit of 3,999
The system has no symbol for zero and no concept of one. It was built for counting and recording rather than calculation, and positional arithmetic (the thing zero makes possible) is not something the notation supports. This is a large part of why it was displaced for computation.
There is also a ceiling. With M as the largest symbol and no more than three repetitions permitted, the largest value in standard notation is 3,999, written MMMCMXCIX. Larger numbers historically used a bar above a numeral to multiply it by a thousand, a convention this converter does not implement.
- Negative numbers and fractions have no standard representation either, though the Romans used a separate duodecimal system for fractions.
- Years, monarch and pope regnal numbers, book chapters, and film copyright dates are where the notation survives.
- Because there is no zero, the numerals cannot express an empty column. The value is read from the symbols present, not from position.
Frequently Asked Questions
Why is 4 written as IV, not IIII?
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Roman numerals use a subtractive shortcut to avoid four-character repetitions. IV (5 minus 1), IX (10 minus 1), XL (50 minus 10) and so on are all subtractive forms. Clock faces sometimes use IIII for symmetry, but the formal rule is IV.
What is the largest number Roman numerals can represent?
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In the standard system, 3,999 (MMMCMXCIX). Larger numbers traditionally use a horizontal bar over a letter to multiply it by 1,000, but that notation is rarely used today and is not supported here.
Is there a Roman numeral for zero?
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No. The Romans had no symbol for zero. Medieval scribes occasionally used "N" (from Latin nullus) for nothing, but it is not part of the standard system.
How do I read a long Roman numeral?
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Read left to right, adding values. When a smaller value precedes a larger one (e.g. IV, IX, XL, CD), subtract it from the next. For example, MCMLXXXIV = 1000 + (1000−100) + 50 + 30 + (5−1) = 1984.