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Roman Numeral Calculator

Convert between Roman numerals and decimal numbers
Enter a number between 1 and 3999.

Enter a decimal number to convert to Roman numerals.

Enter a Roman numeral using I, V, X, L, C, D, M.

Enter a Roman numeral to convert to decimal.

Roman Numerals Guide

Roman Numeral Symbols

Symbol Value Example
I 1 I = 1, II = 2, III = 3
V 5 V = 5, VI = 6, VII = 7
X 10 X = 10, XX = 20, XXX = 30
L 50 L = 50, LX = 60, LXX = 70
C 100 C = 100, CC = 200, CCC = 300
D 500 D = 500, DC = 600, DCC = 700
M 1000 M = 1000, MM = 2000, MMM = 3000

Conversion Rules

1. Additive Principle

When symbols are arranged from largest to smallest, add their values.

Example: VI = V + I = 5 + 1 = 6

2. Subtractive Principle

When a smaller symbol appears before a larger one, subtract it.

Examples:

  • IV = 5 - 1 = 4
  • IX = 10 - 1 = 9
  • XL = 50 - 10 = 40
  • XC = 100 - 10 = 90
  • CD = 500 - 100 = 400
  • CM = 1000 - 100 = 900
3. Repetition Rule

A symbol can be repeated up to 3 times to add value.

Example: III = 1 + 1 + 1 = 3

Historical Facts

  • Ancient Rome: Used for counting and record-keeping throughout the Roman Empire
  • Modern Use: Still used in clocks, book chapters, movie sequels, and Super Bowl numbering
  • No Zero: Romans had no symbol for zero; it was introduced later by Arabic numerals
Quick Tips
  • Reading Order
    Always read Roman numerals from left to right.
  • Common Years
    2024 = MMXXIV, 1999 = MCMXCIX, 2000 = MM
  • Limit
    Standard Roman numerals go up to 3999 (MMMCMXCIX).
Common Numbers
  • 1 = I
  • 4 = IV
  • 9 = IX
  • 40 = XL
  • 90 = XC
  • 400 = CD
  • 900 = CM

Roman Numerals

Roman numerals originated in ancient Rome and remained the usual way of writing numbers throughout Europe well into the Late Middle Ages.

Key Rules
Largest First Write symbols from largest to smallest value
Subtraction Smaller before larger means subtract
Max 3 Repeats Same symbol can't repeat more than 3 times
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Roman Numerals:

Did You Know?

The Romans had no symbol for zero! The concept of zero as a number was introduced much later by Indian mathematicians and spread through the Arabic numeral system.