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Developer ToolsRoman Numeral Converter | Convert Arabic & Roman Numbers
Free online Roman numeral converter. Easily convert between Arabic numbers and Roman numerals (I, V, X, L, C, D, M). Supports numbers 1-3999 with instant conversion and validation.
Arabic to Roman
Roman to Arabic
Valid symbols: I, V, X, L, C, D, M
Roman Numeral Reference
I
1
V
5
X
10
L
50
C
100
D
500
M
1000
MMMCMXCIX
3999 (max)
Key Rules:
- • Symbols are written from largest to smallest, left to right
- • A smaller symbol before a larger one means subtraction (e.g., IV = 4, IX = 9)
- • A smaller symbol after a larger one means addition (e.g., VI = 6, XI = 11)
- • Only I, X, and C can be subtracted, and only from the next two higher values
- • A symbol cannot be repeated more than three times in succession
Related Tools
About Roman Numeral Converter
How It Works
- Convert Arabic numbers (1-3999) to Roman numerals instantly
- Convert Roman numerals back to Arabic numbers
- Automatic validation and error checking
- Real-time conversion as you type
- Support for all standard Roman numeral symbols (I, V, X, L, C, D, M)
Common Use Cases
- Educational purposes and learning Roman numerals
- Historical document analysis and research
- Clock face and watch design
- Book chapter numbering and outlines
- Movie credits and copyright dates
- Event numbering (Super Bowl, Olympics)
Frequently Asked Questions
How do I convert Arabic numbers to Roman numerals?
Simply enter your Arabic number (1-3999) in the "Arabic to Roman" input field, and the converter will instantly display the corresponding Roman numeral. The conversion happens automatically as you type.
How do I convert Roman numerals to Arabic numbers?
Enter your Roman numeral (using letters I, V, X, L, C, D, M) in the "Roman to Arabic" input field. The tool will automatically convert it to an Arabic number and validate the format.
What is the valid range for Roman numeral conversion?
This converter supports numbers from 1 to 3999. Roman numerals traditionally don't have a symbol for zero, and numbers above 3999 require special notation (like a bar over the numeral) that isn't part of the standard Roman numeral system.
What are the basic Roman numeral symbols?
The seven basic Roman numeral symbols are: I (1), V (5), X (10), L (50), C (100), D (500), and M (1000). All other numbers are formed by combining these symbols according to specific rules.
How does the subtraction rule work in Roman numerals?
When a smaller symbol appears before a larger one, it means subtraction. For example, IV = 4 (5-1), IX = 9 (10-1), XL = 40 (50-10), XC = 90 (100-10), CD = 400 (500-100), and CM = 900 (1000-100). Only I, X, and C can be subtracted, and only from the next two higher values.
Can I use lowercase letters for Roman numerals?
Yes, the converter accepts both uppercase and lowercase letters. It will automatically convert your input to uppercase and process it correctly. However, Roman numerals are traditionally written in uppercase.
Why does the converter show an error for some Roman numerals?
The converter validates that the Roman numeral follows proper formation rules. Common errors include: using invalid characters, repeating a symbol more than three times in succession, or using incorrect subtraction combinations. The tool will highlight these errors and provide guidance.
What are some common uses for Roman numerals today?
Roman numerals are still used in many contexts: clock faces, book chapters and outlines, movie sequels and copyright dates (e.g., MMXXIV for 2024), event numbering (Super Bowl LVIII), monarchs and popes (Elizabeth II), building cornerstones, and formal documents.
Can I convert decimal or fractional numbers?
No, Roman numerals only represent whole numbers. The system doesn't have symbols for fractions, decimals, or zero. If you enter a decimal number, the converter will show an error and ask you to enter a whole number.
How do I know if my Roman numeral conversion is correct?
The converter automatically validates Roman numerals by converting them back and checking if they match the input. If you convert a number to Roman and then back to Arabic, you should get the same number. This bidirectional validation ensures accuracy.
What does the "Swap Values" button do?
The Swap Values button transfers the conversion result from one side to the input on the other side. For example, if you converted 42 to XLII, clicking Swap will put XLII in the Roman input field, allowing you to verify the conversion by converting back.
Can this tool help me learn Roman numerals?
Yes! The tool includes a reference table showing all basic symbols and their values, explains the key rules of Roman numeral formation, and provides instant feedback on your inputs. You can practice converting numbers both ways and immediately see if you're correct.