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Roman Numeral Converter: Decimal to Roman and Back

This free Roman numeral converter turns numbers into Roman numerals and Roman numerals back into numbers. It detects the direction itself, checks the numerals for errors and converts a whole list at once.

By Debmedia Technologies LLP · Kolkata, India · Updated

What Is a Roman Numeral Converter?

A Roman numeral converter changes ordinary numbers into Roman numerals, and Roman numerals back into ordinary numbers. Roman numerals still appear in book chapters, film credits, clock faces, building cornerstones, outlines and the names of kings and events. Reading them is easy for short ones, but a year such as MCMXCIV takes a moment to work out.

This Roman numeral converter finds the direction itself: type digits to get a numeral, or type letters to get a number. It checks that numerals are written correctly and converts many lines at once.

How to Use This Converter

  1. Type one number or one Roman numeral per line. You can mix both kinds.
  2. Press Convert.
  3. Read the results in the box, or line by line in the table.
  4. Fix any line marked as an error, then convert again.

The Symbols and Their Values

SymbolValueSymbolValue
I1C100
V5D500
X10M1,000
L50

Symbols are added from left to right, but a smaller symbol placed before a larger one is subtracted. So IV is 4, IX is 9, XL is 40 and CM is 900. The history and rules are summarized in Roman numerals on Wikipedia.

The Rules the Converter Checks

  • A symbol may repeat up to three times in a row. That is why 4 is IV and not IIII.
  • Only I, X and C may be subtracted, and only from the next two larger symbols.
  • V, L and D are never repeated or subtracted.
  • The range is 1 to 3999. There is no zero and no symbol above M.

A numeral that breaks these rules, such as IIII or VX, is reported as invalid, with the reason.

Useful Examples

1994 is MCMXCIV, which is 1000 plus 900 plus 90 plus 4. The year 2024 is MMXXIV. The number 49 is XLIX, because 40 is XL and 9 is IX. Copyright years in film credits are almost always written this way.

To write numbers in words instead, use the number to words converter. To see a number in binary, octal and hex, try the number base converter. If you need to find numbers inside a text first, use the text extractor. Everything runs in your browser.

Read and Write Numerals With Confidence

Roman numerals look simple, yet the subtraction rules trip up many people. The converter does the maths and checks the form, so you know that XLIX is correct and IL is not. Use it for chapter numbers, film years, outlines and tattoos, and always double-check a date before it becomes permanent.

Frequently Asked Questions

I is 1, V is 5, X is 10, L is 50, C is 100, D is 500 and M is 1,000. Smaller symbols before a larger one are subtracted, so IV is 4 and IX is 9.
Standard Roman numerals have no symbol above M and allow it to repeat only three times, so 3999 (MMMCMXCIX) is the largest value. Bigger values use bars above the letters, which this tool does not.
The standard form writes 4 as IV. Clock faces sometimes show IIII, but the tool follows the strict rules used in most writing.
No. The Romans had no symbol for zero, so the converter starts at 1.

Disclaimer: results are calculated in your browser from the numbers you enter. Check important results before you rely on them for money, health, safety or legal decisions.