Roman Numeral Converter
Convert numbers to Roman numerals and Roman numerals back to numbers.
How to use the Roman Numeral Converter
- To convert a number, type any whole number from 1 to 3,999 into the Number field.
- To read a numeral, type it into the Roman numeral field instead — upper or lower case both work.
- The other field fills in as you type; an invalid numeral such as IIII or VX shows an error instead of a wrong answer.
About the Roman Numeral Converter
Roman numerals are the number system used in ancient Rome, still seen today on clock faces, in movie copyright years, for book chapter numbers, and to denote monarchs and Super Bowls (like Super Bowl LVIII). This tool converts in both directions: type a regular number to get its Roman numeral form, or type Roman numerals to get the number back.
The standard system represents values using combinations of seven letters — I, V, X, L, C, D, and M — and supports whole numbers from 1 to 3,999, the practical range for the traditional subtractive notation (like IV for 4 or IX for 9).
Worked example
Example: converting 1994 returns MCMXCIV (1000 + 900 + 90 + 4), and converting the Roman numeral XLII back returns 42.
Reading a Roman numeral step by step
The seven symbols are I (1), V (5), X (10), L (50), C (100), D (500), and M (1000). Read left to right and add each value, except when a smaller symbol comes directly before a larger one — then subtract it. The easiest way to read a long numeral is to split it into thousands, hundreds, tens, and ones: MMXXVI is MM (2000) + XX (20) + VI (6) = 2026, and MCMXCIX is M (1000) + CM (900) + XC (90) + IX (9) = 1999.
The rules for subtraction
Subtraction is only allowed in six combinations, which is where most invented numerals go wrong:
- I can come before V and X only: IV = 4, IX = 9.
- X can come before L and C only: XL = 40, XC = 90.
- C can come before D and M only: CD = 400, CM = 900.
- V, L, and D are never subtracted or repeated, and no symbol appears more than three times in a row.
- So 49 is XLIX (40 + 9), not IL, and 99 is XCIX, not IC.
Why some numerals are rejected
When converting from Roman numerals, this tool accepts only the standard modern form and checks that your input is exactly how the number would normally be written. Forms like IIII, VV, or IC are rejected even though their intended value is guessable. Historical inscriptions and clock faces sometimes use IIII for 4, but the standard form is what you need for dates, outlines, and legal documents.
Frequently asked questions
- Why is there no Roman numeral for zero?
- The Roman numeral system predates the widespread use of zero as a number in Western mathematics — it was designed purely for counting and recording positive quantities, so it has no symbol for zero or negative numbers.
- What's the largest number Roman numerals can represent?
- Using standard notation, 3,999 (MMMCMXCIX) is the practical limit, since numerals aren't repeated more than three times in a row and there's no standard single symbol above M (1,000). Larger numbers historically used a bar over a numeral to multiply it by 1,000, which most modern converters (including this one) don't support.
- Why is 4 written as IV instead of IIII?
- This is 'subtractive notation': placing a smaller numeral before a larger one means subtract it (IV = 5 − 1 = 4) rather than add it. It's the standard modern convention, though IIII does appear historically and is still sometimes used on clock faces for visual symmetry.
- Does this handle lowercase Roman numerals?
- Yes — the numeral-to-number direction accepts lowercase letters (like 'xlii') and treats them the same as uppercase, since case doesn't change the value.