Convert numbers to Roman numerals and back, with strict validation.
A year
Convert to numerals
2026Reading a numeral
A film copyright date
MCMLXXXVIIThe largest value
The limit of standard notation
3999A year
Convert to numerals
2026Reading a numeral
A film copyright date
MCMLXXXVIIThe largest value
The limit of standard notation
3999Number to numeral, or numeral to number. Conversion runs as you type.
Numbers from 1 to 3999, or a numeral using only M, D, C, L, X, V and I.
Invalid numerals are explained, including what the correct form for that value would be.
IIII and IC are rejected, and the error names the correct form — which is genuinely useful when you are learning the rules.
The 3999 ceiling is not arbitrary; the tool explains why plain letters stop there instead of just refusing.
Reading a numeral off a building or a film credit is the more common need, and it is fully supported.
Convert an ordinary number into Roman numerals or read a numeral back as a number. Validation is strict in both directions: IIII and IC are rejected with an explanation of the correct form, because the standard system uses subtractive notation with specific rules rather than any arrangement that happens to add up. The supported range is 1 to 3999, which is the limit of what plain letters can express — larger values historically used overlines that text cannot represent.
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