Roman Numeral Converter
Convert integers to Roman numerals and Roman numerals back to integers.
Convert whole numbers into Roman numerals or translate Roman numerals back into standard numbers, following the traditional subtractive notation rules.
How Roman Numeral Converter Works
To convert a number to Roman numerals, the calculator repeatedly subtracts the largest possible Roman value (starting from 1000 for M down to 1 for I) from your number, appending the matching symbol each time — including the subtractive pairs like CM (900) and IV (4) that avoid writing four identical symbols in a row.
To convert a Roman numeral back to a number, it reads the numeral from left to right, matching the longest valid symbol at each position (checking two-letter subtractive pairs like "IX" before single letters) and adding up each matched value.
Standard Roman numerals only represent whole numbers from 1 to 3999; there is no symbol for zero or for numbers at or above 4000 in this classic notation.
See It In Action
Who Uses Roman Numeral Converter and Why
- Reading a date or edition number shown in Roman numerals, such as on a monument, clock face, or movie credit.
- Converting a chapter or section number for a formally styled document that uses Roman numeral numbering.
- Checking a homework problem on subtractive notation rules (why 4 is IV, not IIII).
- Converting between standard numbers and Roman numerals for things like Super Bowl or Olympic Games numbering.
Mistakes to Avoid
- Writing 4 as IIII instead of IV — standard Roman numerals use subtractive notation specifically to avoid four repeated symbols in a row.
- Entering a number at or above 4000 and expecting a result — standard Roman numerals only cover 1 to 3999 without extended notation like an overline, which this converter doesn't use.
- Expecting a Roman numeral for zero — there is no symbol for zero in standard Roman numeral notation.
Tips for Best Results
- Enter Roman numerals in lowercase or mixed case without worrying about it — input is automatically converted to uppercase before being parsed.
- Remember the practical range tops out at 3999 (MMMCMXCIX) when converting a large number.
Fixing Common Problems
My number won't convert to Roman numerals. — Check that it's between 1 and 3999 — standard Roman numeral notation doesn't support 0 or numbers 4000 and above.
My Roman numeral input isn't being recognized. — Confirm you're only using valid Roman numeral letters (I, V, X, L, C, D, M) — any other character will be rejected.
Terms Explained
Subtractive notation: The Roman numeral convention where a smaller value placed before a larger one means subtraction, such as IV = 5 − 1 = 4.
Roman numeral range: The standard supported range of 1 to 3999, since there's no symbol for zero or numbers 4000 and above in classic notation.