Roman Numeral Converter — Convert Between Roman and Arabic Numbers
Roman numerals appear more often than you might expect. Movie credits show MMXXIV instead of 2024. Clock faces use IV and VIII. Book chapters, legal outlines, and academic papers number sections with I, II, III. The Super Bowl uses Roman numerals for its annual designation. When you encounter MCMLXXXIV and need to know the year, or need to write 2024 in Roman form for a design project, a converter saves the mental arithmetic.
This guide covers how Roman numerals work, the conversion rules, how to implement conversion in code, and where Roman numerals still appear in modern usage.
What Are Roman Numerals?
Roman numerals are a number system from ancient Rome using seven symbols: I (1), V (5), X (10), L (50), C (100), D (500), and M (1000). Numbers are formed by combining symbols additively (VIII = 5+1+1+1 = 8) and subtractively (IV = 5-1 = 4). The subtractive rule applies when a smaller value appears before a larger one: IX=9, XL=40, XC=90, CD=400, CM=900.
You would convert Roman numerals when reading historical dates, copyright years, and clock faces, writing formal document outlines, numbering book chapters and appendices, designing with Roman numeral aesthetics, and solving math or trivia challenges.
How to Convert Roman Numerals with FlipMyCase
- Open the FlipMyCase Roman Numeral Converter.
- Enter a Roman numeral (like XIV) to get the Arabic number (14), or enter a number (like 2024) to get the Roman form (MMXXIV).
- The tool validates input and rejects invalid Roman numeral sequences.
- Copy the converted value.
For converting between number bases (binary, hex, octal), use the Number Base Converter.
Code Examples for Roman Numeral Conversion
JavaScript
// Arabic to Roman
function toRoman(num) {
const values = [1000,900,500,400,100,90,50,40,10,9,5,4,1];
const symbols = ['M','CM','D','CD','C','XC','L','XL','X','IX','V','IV','I'];
let result = '';
for (let i = 0; i < values.length; i++) {
while (num >= values[i]) {
result += symbols[i];
num -= values[i];
}
}
return result;
}
console.log(toRoman(2024)); // MMXXIV
console.log(toRoman(1999)); // MCMXCIX
console.log(toRoman(42)); // XLII
// Roman to Arabic
function fromRoman(str) {
const map = { I:1, V:5, X:10, L:50, C:100, D:500, M:1000 };
let result = 0;
for (let i = 0; i < str.length; i++) {
const current = map[str[i]];
const next = map[str[i + 1]] || 0;
result += current < next ? -current : current;
}
return result;
}
console.log(fromRoman('MMXXIV')); // 2024
console.log(fromRoman('MCMXCIX')); // 1999
console.log(fromRoman('XLII')); // 42
// Validate Roman numeral
function isValidRoman(str) {
return /^M{0,3}(CM|CD|D?C{0,3})(XC|XL|L?X{0,3})(IX|IV|V?I{0,3})$/.test(str);
}
console.log(isValidRoman('MCMXCIX')); // true
console.log(isValidRoman('IIII')); // false (should be IV)
Python
def to_roman(num):
values = [(1000,'M'),(900,'CM'),(500,'D'),(400,'CD'),
(100,'C'),(90,'XC'),(50,'L'),(40,'XL'),
(10,'X'),(9,'IX'),(5,'V'),(4,'IV'),(1,'I')]
result = ''
for value, symbol in values:
while num >= value:
result += symbol
num -= value
return result
def from_roman(s):
values = {'I':1,'V':5,'X':10,'L':50,'C':100,'D':500,'M':1000}
result = 0
for i in range(len(s)):
if i + 1 < len(s) and values[s[i]] < values[s[i+1]]:
result -= values[s[i]]
else:
result += values[s[i]]
return result
print(to_roman(2024)) # MMXXIV
print(to_roman(1999)) # MCMXCIX
print(from_roman('MMXXIV')) # 2024
print(from_roman('MCMXCIX')) # 1999
# Generate a Roman numeral table
for n in [1, 4, 5, 9, 10, 40, 50, 90, 100, 400, 500, 900, 1000]:
print(f'{n:>5d} = {to_roman(n)}')
# Convert year range
for year in range(2020, 2027):
print(f'{year} = {to_roman(year)}')
Go
package main
import "fmt"
func toRoman(num int) string {
values := []int{1000,900,500,400,100,90,50,40,10,9,5,4,1}
symbols := []string{"M","CM","D","CD","C","XC","L","XL","X","IX","V","IV","I"}
result := ""
for i, v := range values {
for num >= v {
result += symbols[i]
num -= v
}
}
return result
}
func fromRoman(s string) int {
m := map[byte]int{'I':1,'V':5,'X':10,'L':50,'C':100,'D':500,'M':1000}
result := 0
for i := 0; i < len(s); i++ {
if i+1 < len(s) && m[s[i]] < m[s[i+1]] {
result -= m[s[i]]
} else {
result += m[s[i]]
}
}
return result
}
func main() {
fmt.Println(toRoman(2024)) // MMXXIV
fmt.Println(fromRoman("MMXXIV")) // 2024
}
Real-World Use Cases
Movie and media copyright years. Film credits and media copyright notices use Roman numerals. "© MMXXIV" means 2024. Convert quickly with the Roman Numeral Converter when you need to verify a copyright date.
Document and outline formatting. Legal briefs, academic papers, and business reports use Roman numerals for major sections: I. Introduction, II. Background, III. Analysis. Convert section numbers when reorganizing outlines.
Design and branding. Architectural cornerstones, luxury watch faces, and premium branding use Roman numerals for aesthetic value. Generate the Roman form of years, anniversaries, and significant numbers for design projects.
Education and puzzles. Teaching Roman numerals is part of math curricula. The converter serves as both a learning tool and answer checker. Crossword and trivia puzzles frequently require Roman numeral knowledge.
Common Mistakes and Gotchas
The subtractive rule only applies to specific pairs. IV (4), IX (9), XL (40), XC (90), CD (400), and CM (900) are the only valid subtractive combinations. "IC" for 99 is not valid — the correct form is XCIX (90+9). The Roman Numeral Converter validates input and rejects non-standard forms.
Roman numerals have no zero. The Roman system has no symbol for zero and no concept of place value. This is one reason it was eventually replaced by the Hindu-Arabic system for mathematics.
Standard Roman numerals max out at 3999 (MMMCMXCIX). Numbers above this require extended notation — a bar over a letter multiplies its value by 1000. This notation is rare in modern usage.
IIII vs IV on clock faces is a deliberate design choice, not an error. Many clocks use IIII for 4 instead of IV for visual balance — the IIII matches the VIII on the opposite side. Both are considered acceptable in horology.
Frequently Asked Questions
How do I write the current year in Roman numerals? Enter the year into the Roman Numeral Converter. For example, 2026 is MMXXVI (1000+1000+10+10+5+1). The tool handles any year from 1 to 3999.
What is the longest Roman numeral under 4000? 3888 = MMMDCCCLXXXVIII — 15 characters. It uses every additive symbol multiple times without any subtractive combinations.
Can Roman numerals represent decimals or fractions? Not in the standard system. Romans used a separate fraction system based on twelfths (uncia). For decimal conversion, use the Number Base Converter which handles decimal, binary, hex, and octal.
Conclusion
Roman numeral conversion bridges ancient notation and modern usage. From movie credits and clock faces to legal documents and design projects, Roman numerals appear frequently enough that quick conversion is a practical skill.
The FlipMyCase Roman Numeral Converter handles bidirectional conversion with validation for values 1 through 3999. For other number systems, use the Number Base Converter. For programmatic conversion, the JavaScript, Python, and Go examples above implement both directions with clean, efficient algorithms.