Roman Numeral Converter
Type a number or a Roman numeral and get the conversion both ways, with a breakdown of the symbols used — all in your browser.
Auto-detects direction. Supports 1–3,999,999.
How to use Roman Numeral Converter
The Roman numeral converter converts instantly in both directions: type an Arabic number (1–3,999,999) to get its Roman numeral, or type a Roman numeral to get the Arabic value. The tool also shows a symbol-by-symbol breakdown so you can see exactly how each numeral contributes to the total. For numbers above 3,999, parenthesis notation is used to represent thousands-multiples (e.g. (IV) = 4,000), consistent with the extended vinculum convention.
- Type a number (e.g. 2024) or a Roman numeral (e.g. MCMXCIV) in the input box.
- The tool auto-detects whether you entered a number or a Roman numeral.
- Click Convert (or press Enter) to see the result.
- Expand the Symbol Breakdown table to see the value of each numeral token.
Your data never leaves your device — 100% private processing.
Roman numeral rules and subtractive notation
Roman numerals are formed by combining seven base symbols and applying two rules. Additive rule: identical or smaller symbols placed after a larger one are added (VI = 6, XV = 15). Subtractive rule: a smaller symbol placed immediately before a larger one is subtracted (IV = 4, IX = 9, XL = 40, XC = 90, CD = 400, CM = 900). Only these six subtractive pairs are valid; writing IIX for 8 or VL for 45 is not standard. A symbol may not be repeated more than three times consecutively (so 4 must be IV, not IIII).
| Symbol | Value | Notes |
|---|---|---|
| I | 1 | Can be repeated up to 3 times |
| V | 5 | Cannot be repeated |
| X | 10 | Can be repeated up to 3 times |
| L | 50 | Cannot be repeated |
| C | 100 | Can be repeated up to 3 times |
| D | 500 | Cannot be repeated |
| M | 1,000 | Can be repeated up to 3 times (standard); parentheses for thousands above |
Extended Roman numerals beyond 3,999
The standard Roman system tops out at 3,999 (MMMCMXCIX). To represent larger numbers, the historical vinculum convention placed a bar (overline) above a numeral to multiply it by 1,000. This tool uses parentheses as a typographically safe equivalent: (V) = 5,000; (X) = 10,000; (L) = 50,000; (C) = 100,000; (D) = 500,000; (M) = 1,000,000. Combined with a suffix: (III)DCCCXCIX = 3,899 in thousands, i.e. 3,899,000. Roman numerals above 3,999 appear in historical contexts such as clock faces, book volumes, and film copyright notices.
Glossary
- Subtractive notation
- Placing a smaller numeral before a larger one to indicate subtraction (e.g. IV = 4, CM = 900).
- Additive notation
- Placing numerals of equal or decreasing value together to indicate addition (e.g. VI = 6).
- Vinculum
- A horizontal bar over a Roman numeral that multiplies its value by 1,000, used for numbers above 3,999.
- ASCII-safe notation
- Using parentheses around a Roman numeral to represent the vinculum in text: (V) = 5,000.
Related reading
Frequently Asked Questions
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Why use Roman Numeral Converter?
- Step-by-step explanations alongside every calculation
- Printable or shareable result summaries
- Works entirely offline in your browser
- Built-in input validation prevents common mistakes
Common use cases
- Calculate loan repayments before applying
- Check compound interest on savings accounts
- Estimate tax owed before filing
- Work out break-even point for a new business
- Plan retirement savings contributions
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