Roman Numeral Converter
Convert between Arabic numbers and Roman numerals (1–3999) instantly, in both directions.
Standard notation only: whole numbers 1–3999. Zero and negative numbers have no standard form; vinculum notation is not supported.
Common year reference
| Year | Roman | Note |
|---|
Spell it out? Number to words · format years: Number formatter · other bases: Base converter.
Convert between Arabic numbers (1–3999) and Roman numerals in both directions: type 2026 and read MMXXVI; type MCMXCIX and read 1999. The converter enforces canonical (standard subtractive) form and tells you why an invalid string fails instead of guessing.
The rules in one breath: seven symbols (I=1, V=5, X=10, L=50, C=100, D=500, M=1000); repeat I, X, C, M at most three times; V, L, D never repeat; subtractive pairs are exactly IV, IX, XL, XC, CD, CM. That is why 1999 is MCMXCIX (M + CM + XC + IX) and never IMM — each subtractive prefix may only precede the next two symbol steps.
Boundaries: the canonical system covers 1–3999 only — there is no standard single-character way to write 4000+ (historic texts used an overline for ×1000, which plain text cannot carry), and there is no Roman zero: the numeral system simply has no symbol for it (medieval scribes wrote the word “nulla”). Inputs like IIII are rejected as non-canonical even though you may see IIII on clock faces — that is a deliberate watchmaking tradition, not standard notation.
Worked example: 2026 = MM (2000) + XX (20) + VI (6) → MMXXVI. Reading back: scan left to right, add each symbol, but subtract when a smaller symbol precedes a larger one — M(1000) + M(1000) + X(10) + X(10) + V(5) + I(1) = 2026.
Published test vectors — each validated against the live tool: 2026 ↔ MMXXVI · 1999 ↔ MCMXCIX · LIV ↔ 54 · 3999 (MMMCMXCIX) is the accepted maximum · IIII is rejected as non-canonical with the number field cleared rather than showing a ghost value. Last verified: 2026-08-12.
FAQ
Why is 1999 MCMXCIX and not IMM or MIM?
Subtractive notation is restricted to six exact pairs: IV, IX, XL, XC, CD, CM. I may only precede V or X — never M. So 1999 decomposes as M (1000) + CM (900) + XC (90) + IX (9). Shortcuts like IMM look clever but were never part of the canonical system.
Why do clocks show IIII instead of IV?
Watch and clock faces traditionally use IIII for visual balance with the VIII on the opposite side — a design convention dating back centuries. In standard notation IIII is invalid: I repeats at most three times, so 4 is always IV.
Why does it stop at 3999?
Because M can repeat at most three times and there is no bigger single symbol. Historic texts drew an overline (vinculum) over a numeral to multiply it by 1000, but plain text and most fonts cannot represent that reliably, so canonical converters cap at MMMCMXCIX = 3999.
Is there a Roman numeral for zero?
No. The Roman system predates the concept of zero as a numeral; medieval scholars wrote the Latin word “nulla” or N where zero was needed. That is why this converter’s range starts at 1.
Does case matter when I type a Roman numeral?
No — mmxxvi and MMXXVI are read the same. The converter normalizes case before validating, and output is always uppercase, which is the conventional written form.
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