Number to Roman Converter Number to Roman Converter

Decimal Number

e.g. 11

Roman Numeral

e.g. XI

Note: You can also input Roman Numeral to convert to Number



About Roman Numerals

Roman numerals are represented by seven different symbols: I, V, X, L, C, D and M.

Symbol       Value
I             1
V             5
X             10
L             50
C             100
D             500
M             1000

These symbols can be combined like this to create numbers:

123456789
IIIIIIIVVVIVIIVIIIIX
102030405060708090
XXXXXXXLLLXLXXLXXXXC
100200300400500600700800900
CCCCCCCDDDCDCCDCCCCM

Things to note about roman numerals:

  • When a symbol appears after a larger (or equal) symbol it is added
    Example: VI = V + I = 5 + 1 = 6
    Example: LXX = L + X + X = 50 + 10 + 10 = 70
  • But if the symbol appears before a larger symbol it is subtracted
    Example: IV = V − I = 5 − 1 = 4
    Example: IX = X − I = 10 − 1 = 9
  • I can be placed before V (5) and X (10) to make 4 and 9.
  • X can be placed before L (50) and C (100) to make 40 and 90.
  • C can be placed before D (500) and M (1000) to make 400 and 900.


Romanize Number

Javascript method used in this converter to convert from Decimal Number to Roman:-

const romanize = (number) => {
  const lookup = {M:1000,CM:900,D:500,CD:400,C:100,XC:90,L:50,XL:40,X:10,IX:9,V:5,IV:4,I:1};
  let roman = '';

  for (let i in lookup ) {
    while ( number >= lookup[i] ) {
      roman += i;
      number -= lookup[i];
    }
  }
  return roman;
}


Roman to Decimal Number

Javascript method used in this converter to convert from Roman to Decimal Number:-

const romanToInteger = (roman) => {
  const lookup = {M:1000,CM:900,D:500,CD:400,C:100,XC:90,L:50,XL:40,X:10,IX:9,V:5,IV:4,I:1};
  const array = roman.split('');
  let total = 0, current, currentValue, next, nextValue;
  
  for(let i=0; i<array.length; i++){
    current = array[i];
    currentValue = lookup[current];
    next = array[i+1];
    nextValue = lookup[next];

    if(currentValue < nextValue) {
      total -= currentValue;
    }else {
      total += currentValue;
    }
  }
  return total;
}