1. What does this tool do
This free online Roman numeral converter converts between Arabic numbers (1–3999) and Roman numerals in standard subtractive notation (e.g. IV, XL, MCMXCIX). Use it to convert to Roman numerals or Roman to number for education, outlines, or quick reference. Instant, free, and private—no sign-up, all in your browser. Ideal for school, outlines, clocks/copyright years, or puzzles.
2. How to use it
Quick start: Enter an Arabic number (1–3999) or a Roman numeral (e.g. XIV, MCMXCIX). See the equivalent in the other system and copy if needed.
- Enter a value — Type an Arabic number (1–3999) or a Roman numeral (e.g. XIV, MCMXCIX).
- See the result — The tool shows the equivalent in the other system. Invalid or out-of-range input is reported.
- Copy — Copy the result if needed for documents or lessons.
3. How it works
Arabic → Roman: The tool maps thousands, hundreds, tens, and ones to Roman symbols (M, D, C, L, X, V, I) using subtractive notation (e.g. 4 → IV, 9 → IX). Roman → Arabic: The string is parsed left to right, adding or subtracting values according to the standard rules. All processing is client-side in your browser. No data is sent to any server.
4. Use cases & examples
- School — Convert numbers for history or Latin class.
- Outlines — Use Roman numerals for section numbering (I, II, III, IV…).
- Clocks or copyright — Decode or encode years (e.g. MMXXIV for 2024).
- Puzzles — Quick conversion for crosswords or games.
Example
- 2024 → MMXXIV
- XLII → 42
- MCMXCIX → 1999
5. Limitations & known constraints
- Range — Only 1–3999. Classical Roman numerals do not have a standard for zero or numbers above 3999 in common use.
- Notation — Standard subtractive notation only (e.g. IV not IIII for 4). Non-standard forms may not parse correctly.
- Input — Roman input is case-insensitive in most implementations (e.g. "iv" and "IV" both mean 4).