| Roman | Value | Roman | Value |
|---|---|---|---|
| I | 1 | L | 50 |
| IV | 4 | XC | 90 |
| V | 5 | C | 100 |
| IX | 9 | CD | 400 |
| X | 10 | D | 500 |
| XL | 40 | CM | 900 |
| M | 1000 | MMMCMXCIX | 3999 |
How to Convert Roman Numerals
Roman numerals are still used today in clock faces, book chapters, film sequels, sporting events, and formal documents. Understanding how to read and write them is a useful skill, and this converter makes the process instant and error-free.
How to Use This Converter
- Type a number or Roman numeral into the input field. The converter automatically detects whether you have entered digits or letters.
- View the result in the blue result box. If you entered a number, you will see the Roman numeral equivalent. If you entered a Roman numeral, you will see the Arabic number.
- Use the reference table below the input to quickly look up common Roman numeral values.
- Copy the result by clicking the Copy button to use the conversion elsewhere.
How It Works
For number-to-Roman conversion, the algorithm repeatedly subtracts the largest possible Roman numeral value from the number and appends the corresponding symbol. It uses a lookup table of 13 values from M (1000) down to I (1), including subtractive forms like CM (900), CD (400), XC (90), XL (40), IX (9), and IV (4). For Roman-to-number conversion, the algorithm reads each character and checks if the next character represents a larger value — if so, it subtracts the current value; otherwise, it adds it. This handles the subtractive rule automatically. All processing runs locally in your browser.
Frequently Asked Questions
How do Roman numerals work?
Roman numerals use seven symbols: I (1), V (5), X (10), L (50), C (100), D (500), and M (1000). Symbols are added when placed after a larger numeral and subtracted when placed before. For example, IV is 4 (5 minus 1) and VI is 6 (5 plus 1).
What is the largest number in Roman numerals?
Using standard Roman numerals without special notation, the largest number is 3999 (MMMCMXCIX). Numbers above 3999 require a bar notation (vinculum) where a line above a numeral multiplies its value by 1000. This converter supports 1 to 3999.
Why is 4 written as IV instead of IIII?
The subtractive rule prevents four identical symbols in a row. IV means 5 minus 1 (4), which is more concise than IIII. However, some clock faces traditionally use IIII for 4 instead of IV, which is an accepted historical variation.
How do I convert a year to Roman numerals?
Break the year into thousands, hundreds, tens, and ones, then convert each part. For example, 2024 is MM (2000) + XX (20) + IV (4) = MMXXIV. Our converter handles this automatically — just type the year.
Is there a Roman numeral for zero?
No, the Roman numeral system has no symbol for zero. The concept of zero as a number did not exist in ancient Rome. The word nulla (meaning nothing) was sometimes used, but there is no standard Roman numeral representation for zero.
What are the basic Roman numeral rules?
The three main rules are: symbols are generally written largest to smallest from left to right; a smaller symbol before a larger one means subtraction (IV = 4); and no symbol should appear more than three times in a row. Additionally, only I, X, and C can be used as subtractive prefixes.