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Roman Numerals Converter Online
Free Roman numerals converter between Arabic numbers (1–3999) and Roman numerals.
Roman numerals, and where they go wrong
Roman numerals are additive with one subtractive rule: I, X, C and M may precede a larger symbol to subtract from it, while V, L and D never do. That single exception is why 4 is IV and 9 is IX, and why 45 is XLV rather than VL.
Standard form stops at 3999, because there is no symbol above M and the historical overline notation for larger values is not part of the common form. A converter that accepts 4000 is either using that overline convention or quietly producing something no reader will interpret as intended.
Watch case and context. A lowercase i in a legal document is a sub-item rather than the number one, and a pair of Ms in a name is a name rather than 2000. Convert deliberately instead of pattern-matching every string that looks Roman, and normalise case before comparing.
FAQ
- What range is supported?
- Standard notation up to 3999.
- Case sensitive?
- Roman input is normalized to uppercase.
- Uploaded?
- No.
- Why is 4 written IV and not IIII?
- The subtractive rule is the standard form, and IV is what a modern reader expects. Clock faces are the well-known exception and traditionally use IIII, which is why you will still see it on dials; in text and in code, use IV.
- What is the largest Roman numeral?
- 3999, written MMMCMXCIX in standard form. Beyond that you need the overline convention, where a bar multiplies a symbol by a thousand, and that notation is not portable enough to rely on outside a historical or decorative context.
- How do I write a year in Roman numerals?
- Convert the thousands, then the hundreds, then the tens and units, and concatenate: 2026 becomes MM for the thousands and XXVI for the remainder. Reading them back is the same process in reverse, which is why a year is easier to verify than an arbitrary large number.