Convert
Roman numeral converter
Standard subtractive notation only: IV, IX, XL, XC, CD, CM. A string like IIII is reported as invalid rather than quietly turned into 4, which matters when you are checking a date carved on a building.
How to use it
- Type either a number or a Roman numeral.
- The other form appears immediately.
- Valid range is 1 to 3999 — classical notation has no zero or negatives.
- Spaces and full stops are ignored, so “MCMXCIV.” parses the same as “MCMXCIV”.
A number system without zero or place value
Roman numerals are additive with subtractive shortcuts: XIII is ten plus three, IV is five minus one. There is no symbol for zero and no positional notation, which means arithmetic on them is genuinely difficult — multiplying XLII by XVII requires an abacus or a conversion, and medieval merchants did exactly that. The system survived for record-keeping and inscriptions, not for calculation.
Why the subtractive rule exists
IIII was common on clock faces and in Roman inscriptions; IV became standard later, partly because it is shorter. The rule that a smaller symbol may only precede a larger one when it is a power of ten, and only once, is what keeps representations unique — without it, 8 could be VIII, IIX or even IIIIV. Uniqueness is the point.
Where you still meet them
Copyright years on film and television, clock faces, monarchs and popes, Super Bowl numbers, and the occasional building dedication. Clock faces are the interesting case: most use IIII for four rather than the standard IV, a convention that predates the subtractive notation and survives because it balances visually against VIII on the opposite side.
Converter ranges stop at 3,999 because the standard notation has no symbol above M. Anything larger was historically written with an overline, multiplying the value by a thousand — a notation this tool does not attempt.
Frequently asked questions
Why does it stop at 3999?
Classical Roman notation has no symbol for 5000, so numbers above 3999 would need an overline convention that browsers render inconsistently. Everything in that range is unambiguous.
Why is IIII rejected?
IIII was used on clock faces but is not standard notation. This tool follows the standard subtractive rules, so 4 is IV. That makes it useful for validating rather than merely decoding.
Can it read lowercase input?
Yes, mcmxciv is accepted and normalised to uppercase.
Does it handle the zero?
No — there is no Roman numeral for zero. The input 0 returns a range error, which is historically correct.
Why does 4 render as IIII on some clocks?
A casting convention from before the subtractive rule became standard, kept because IIII balances VIII visually opposite it on the dial.
What is the largest number that can be written?
3,999 with standard symbols. Historically larger values used an overline to mean ×1,000, which is not part of the modern notation.