๐๏ธ Roman Numeral Converter
Convert Arabic numbers (1โ3999) to Roman numerals and back. Useful for figuring out what a Roman numeral on a clock face, in movie credits, or in a book's chapter number actually means.
How to use
- Choose the "Number โ Roman" or "Roman โ Number" tab.
- Enter the number or Roman numeral you want to convert.
- The converted result is shown automatically.
How the calculation works
Roman numerals write numbers by combining seven letters: I (1), V (5), X (10), L (50), C (100), D (500) and M (1000). Number to Roman: take the largest values first and repeat each symbol as many times as it fits. 4, 9, 40, 90, 400 and 900 use subtractive notation โ a smaller symbol before a larger one โ as IV, IX, XL, XC, CD and CM. Roman to number: read left to right, subtracting any symbol smaller than the one after it and adding the rest. The result is then converted back to Roman and must match the input exactly, so non-standard forms such as "IIII" or "VX" are rejected. The supported range is 1 to 3999.
Worked example
2026 โ MMXXVI (1000 + 1000 + 10 + 10 + 5 + 1) 1994 โ MCMXCIV (1000 + 900 + 90 + 4) 3999 โ MMMCMXCIX (the maximum) XLII โ 42 (XL = 40, II = 2) IIII โ invalid (the standard form is IV)
Things to be aware of
- Roman numerals have no symbol for zero, and 3999 is the largest number in the standard notation.
- Clock faces traditionally show 4 as IIII rather than IV.
- They are still used for film copyright years, book volumes, Super Bowl numbers and monarchs' regnal numbers.
FAQ
What number range is supported?
Integers from 1 to 3999, since standard Roman numeral notation can't represent 4000 or higher with a single symbol set.
Does it recognize lowercase Roman numerals?
Yes, input is automatically converted to uppercase before being evaluated.
What happens if I enter an invalid Roman numeral?
An error is shown if the string doesn't follow standard Roman numeral notation.