Roman Numeral Converter
Convert any whole number from 1 to 3999 into Roman numerals, or decode a Roman numeral back into a number.
Last updated: June 20, 2026 · Reviewed by TG we-Calculate Editorial TeamDirection
Roman numerals use the symbols I, V, X, L, C, D and M.
How do you convert a number to Roman numerals?
Break the number into thousands, hundreds, tens and units, then write each part with the largest Roman symbols that fit: M, D, C, L, X, V and I. Use subtractive pairs (IV, IX, XL, XC, CD, CM) for 4s and 9s. Standard Roman numerals cover 1 to 3999.
Formula
How this is calculated
Roman numerals are not positional like our decimal system: each symbol has a fixed value (I=1, V=5, X=10, L=50, C=100, D=500, M=1000) and you build a number by adding values from largest to smallest. To turn a number into a numeral, the converter scans a table of 13 building blocks ordered from M (1000) down to I (1), and at each step subtracts the largest block that still fits, appending its symbol — a greedy method that always yields the canonical form. The four subtractive pairs (CM=900, CD=400, XC=90, XL=40) and (IX=9, IV=4) are included so 4s and 9s are written as IV/IX rather than long runs like IIII.
To decode a numeral back to a number, it reads the symbols left to right: normally values are summed, but when a smaller symbol precedes a larger one (the subtractive rule) that smaller value is subtracted instead.
The valid range is 1 to 3999. There is no symbol for zero or negatives, and M can repeat at most three times, so 3999 (MMMCMXCIX) is the ceiling. Input is validated against a strict pattern, so malformed numerals like IIII or VX are rejected rather than silently guessed.
Examples
| Input | Result |
|---|---|
| 2026 → Roman | MMXXVI |
| 49 → Roman | XLIX |
| MCMLXXXIV → Number | 1984 |
Frequently asked questions
Standard Roman numerals use M for 1000 and allow at most three repeats, so MMMCMXCIX = 3999 is the largest value. Higher numbers need a vinculum (overline) that is not part of the basic notation.
No. The Roman system has no symbol for zero, so the smallest value you can convert is 1 (I).
When a smaller symbol comes before a larger one it is subtracted: IV is 4, IX is 9, XL is 40, XC is 90, CD is 400 and CM is 900. This avoids long runs like IIII.
Also known as
Sources & references
TG we-Calculate Editorial Team. (2026). Roman Numeral Converter [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/roman-numeral-converter
TG we-Calculate Editorial Team. "Roman Numeral Converter." TG we-Calculate. 2026. https://we-calculate.com/calculator/roman-numeral-converter.
TG we-Calculate Editorial Team, "Roman Numeral Converter," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/roman-numeral-converter
@misc{wecalculate_roman_numeral_converter, title = {Roman Numeral Converter}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/roman-numeral-converter}}, year = {2026}, note = {TG we-Calculate} }
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