Roman Numeral Converter
Convert between Arabic numbers and Roman numerals.
Decimal → Roman
Roman → Decimal
Roman Numeral Reference
I
1
V
5
X
10
L
50
C
100
D
500
M
1000
IV = 4
IX = 9
XL = 40
XC = 90
CD = 400
CM = 900
Code Examples
function toRoman(num) {
const map = [
['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 result = '';
for (const [roman, value] of map) {
while (num >= value) {
result += roman;
num -= value;
}
}
return result;
}Frequently Asked Questions
How do Roman numerals work?
I=1, V=5, X=10, L=50, C=100, D=500, M=1000. Add values left to right, except when a smaller value precedes a larger (IV=4, IX=9, XL=40, XC=90, CD=400, CM=900).
What's the largest Roman numeral?
Standard notation goes up to 3999 (MMMCMXCIX). For larger numbers, a bar over a numeral multiplies by 1000 (V̄ = 5000), but this isn't commonly used.