The Roman Numeral Converter converts decimal numbers (1โ€“3999) to Roman numerals and vice versa โ€” instantly showing the conversion in both directions.

Roman Numeral Converter

Convert between Arabic numbers and Roman numerals.

Result
โ€”

How to Use This Calculator

  1. Select Number โ†’ Roman to convert a decimal number to Roman numerals, or Roman โ†’ Number to convert a Roman numeral string to a decimal.
  2. Enter your value in the appropriate field.
  3. Click Convert.

Roman Numeral Symbols

Symbol Value
I 1
V 5
X 10
L 50
C 100
D 500
M 1,000

The Subtractive Notation Rule

When a smaller symbol precedes a larger one, it is subtracted rather than added. For example: IV = 5โˆ’1 = 4, IX = 10โˆ’1 = 9, XL = 50โˆ’10 = 40, XC = 90, CD = 400, CM = 900. This rule prevents awkward sequences like IIII (4 written as IV instead).

Frequently Asked Questions

Why only up to 3,999?

Standard Roman numerals represent 1โ€“3,999 using the symbols I through M. Numbers 4,000 and above require a bar (vinculum) over a symbol to multiply it by 1,000 โ€” a convention not universally supported. MMMCMXCIX (3,999) is the largest number representable with standard symbols.

Where are Roman numerals still used today?

Clock faces (XII, IX), movie sequels (Rocky II, III), year of production in films, book chapters, Super Bowl numbers (Super Bowl LVIII), academic outlines, and names with the same given name across generations (Henry VIII, Charles III).

How it works

To convert decimal to Roman: the algorithm iterates through value-symbol pairs from largest to smallest (M=1000, CM=900, D=500...) and greedily appends symbols while the number is large enough. To convert Roman to decimal: each symbol's value is added; if a symbol is followed by a larger one, it is subtracted instead.

Formula

Decimal โ†’ Roman: greedy subtraction from highest value. Roman โ†’ Decimal: sum each symbol value; subtract if the next symbol is larger.