Roman Numeral Converter
Convert Arabic numbers (1-3999) to Roman numerals and back. Our bidirectional converter shows a detailed step-by-step breakdown of each conversion so you can see exactly how Roman numerals work. History of recent conversions included.
Convert between Arabic numbers (1-3999) and Roman numerals bidirectionally. See a detailed step-by-step breakdown of each conversion and browse your recent conversions.
Roman Numeral Reference Table▼
Roman numerals use combinations of these symbols. Smaller values before larger ones indicate subtraction (e.g., IV = 4).
Conversion History (0)
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Supports values from 1 to 3999 (MMMCMXCIX). All conversion logic runs locally in your browser.
Bidirectional Conversion
Convert Arabic numbers to Roman numerals and Roman numerals back to numbers. Swap between modes with one click.
Step-by-Step Breakdown
See exactly how each conversion works with a detailed step-by-step breakdown. Learn the logic behind Roman numeral construction.
Conversion History
Your last 50 conversions are saved automatically. Click any past conversion to reload it instantly.
One-Click Copy
Copy any conversion result to your clipboard with a single click. Perfect for quick reuse in documents or code.
History & Classics Studies
Quickly convert dates, chapter numbers, and references found in historical texts, classic literature, and academic papers.
Math Education
Teach students how Roman numerals work with the step-by-step breakdown. See the subtraction and addition rules in action.
Movie & Event Years
Convert movie copyright years (MMXXIV), Super Bowl numbers (LVIII), and event year notations found in titles and branding.
Programming & Data
Generate Roman numerals for numbering in code comments, documentation outlines, or formatting chapter headings in apps.
Writing & Publishing
Format preface pages, chapter numbers, and front matter in books, theses, and academic publications using proper Roman numerals.
Quick Reference Tool
Keep the converter handy for daily use - decipher clock faces, building dates, monument inscriptions, and copyright notices.
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Frequently Asked Questions
What is the largest number I can convert?
The converter supports numbers from 1 to 3,999 (MMMCMXCIX). Numbers 4,000 and above typically require a vinculum (a bar over the numeral to multiply it by 1,000), which cannot be represented with standard Unicode characters.
Why is 4 written as IV and not IIII?
The subtractive principle - placing a smaller numeral before a larger one to subtract it - is the modern standard for Roman numerals. IV (5-1) is the standard representation for 4. While IIII was sometimes used historically (especially on clock faces), IV is the universally accepted modern form.
Are there rules for valid Roman numerals?
Yes. The converter validates using standard rules: I, X, C, and M can be repeated up to three times (III = 3, XXX = 30). V, L, and D cannot be repeated. Only one smaller numeral can precede a larger one (IV = 4, but IIV is invalid). The converter round-trips each input to ensure validity.
What is the step-by-step breakdown?
For number-to-Roman conversion, the breakdown shows which value is subtracted at each step and which symbol is added. For Roman-to-number conversion, it shows each character's value and whether it's added or subtracted based on the character that follows.
Does this tool work offline?
Yes. All conversion logic runs locally in your browser using JavaScript. No data is sent to any server, and the tool works completely offline after the initial page load.
Is my conversion data stored anywhere?
Your conversion history is stored in your browser's localStorage for your convenience. No data is ever sent to any server, API, or third party. You can clear the history at any time.
What is the subtractive principle?
The subtractive principle means placing a smaller Roman numeral before a larger one to indicate subtraction. For example, IX means 10 - 1 = 9, and CD means 500 - 100 = 400. This system avoids writing four identical symbols in a row and makes numerals more compact.
Can I convert Roman numerals I find online?
Yes. Simply paste or type any Roman numeral into the converter and it will validate and convert it. The tool handles standard modern Roman numerals including common edge cases and invalid combinations.