Roman Numeral Converter
Convert between numbers and Roman numerals instantly. Supports 1-3999 with validation, batch mode, and a quick-reference table.
Reference Table
| Decimal | Roman |
|---|---|
| 1 | I |
| 4 | IV |
| 5 | V |
| 9 | IX |
| 10 | X |
| 40 | XL |
| 50 | L |
| 90 | XC |
| 100 | C |
| 400 | CD |
| 500 | D |
| 900 | CM |
| 1000 | M |
Subtractive Notation Rules
Roman numerals normally add values left to right (e.g. VIII = 8). When a smaller-value numeral appears before a larger one, it is subtracted instead. Only specific pairs are allowed:
- IV = 4 IX = 9(I before V or X)
- XL = 40 XC = 90(X before L or C)
- CD = 400 CM = 900(C before D or M)
No numeral may repeat more than three times consecutively (e.g. III is valid, IIII is not — use IV instead).
How to use
- 1
Choose a direction
Select Number to Roman or Roman to Number using the tabs.
- 2
Enter your value
Type a number (1-3999) or a Roman numeral string.
- 3
Read the result
The conversion appears instantly below the input.
Frequently asked questions
What range is supported?
How does subtractive notation work?
Is my data sent anywhere?
Convert numbers to Roman numerals and back instantly. Enter a decimal
number to see its Roman representation, or type Roman numerals to get
the decimal value. Batch mode lets you convert a list of values at
once. A year mode quickly converts years. Includes a full reference
table and explains the subtractive notation rules. Runs entirely in
your browser.