♚ Roman Numeral Converter
Convert between Arabic numbers and Roman numerals. Supports values from 1 to 3999. Click any result to copy.
Last updated: May 21, 2026 · By Λ
Common Roman numerals
| Roman | Number | Notes |
|---|---|---|
| I | 1 | One unit |
| V | 5 | Five |
| X | 10 | Ten |
| L | 50 | Fifty |
| C | 100 | From the Latin centum |
| D | 500 | Five hundred |
| M | 1000 | From the Latin mille |
| IV | 4 | Subtractive: one before five |
| IX | 9 | Subtractive: one before ten |
| XL | 40 | Ten before fifty |
| XC | 90 | Ten before one hundred |
| CD | 400 | Hundred before five hundred |
| CM | 900 | Hundred before one thousand |
| MCMXCIX | 1999 | The longest common example |
| MMXXVI | 2026 | This year |
Convert Roman numerals both ways
Roman numerals show up in copyright dates on movie credits, regnal names for monarchs and popes, Super Bowl numbering, book chapter headings, and clock faces. They are not used for arithmetic, but they are common enough that decoding one quickly is useful. This converter accepts either side: type an Arabic number on the left to see its Roman form, or type a Roman numeral on the right to see its Arabic value. Both directions validate the input and show a clear message if something is malformed.
The Roman numeral system uses seven letters: I (1), V (5), X (10), L (50), C (100), D (500), and M (1000). Larger values are written by placing letters together, with the value being the sum. To avoid four-in-a-row letters like IIII for 4, the system uses subtractive pairs: IV for 4, IX for 9, XL for 40, XC for 90, CD for 400, and CM for 900. The largest value this converter handles is 3999 (MMMCMXCIX), which is the practical limit of the standard form. Anything above that requires overlines or alternative notations that this tool does not support.
How to use this tool
- Type an Arabic number (1 to 3999) on the left side to see the Roman form.
- Type a Roman numeral on the right side to see its Arabic value. Case does not matter.
- Click any result to copy it to your clipboard.
- Use the reference table below for common values.
Frequently Asked Questions
Why is 4 written as IV instead of IIII?
Standard modern Roman numeral notation uses subtractive pairs to avoid more than three of the same letter in a row. So 4 is IV, not IIII. Historically, IIII did appear on clock faces and in older Latin inscriptions, but it is no longer the accepted form for most uses.
What about zero?
The classical Roman system has no symbol for zero. Medieval scholars used the word nulla or the letter N when they needed a zero, but it is not part of standard notation. This tool only accepts values from 1 to 3999.
Can it parse lowercase roman numerals?
Yes. The input is uppercased before parsing, so "mcmxcix" and "MCMXCIX" both convert to 1999.
What about numbers larger than 3999?
The standard form runs out at 3999. Larger numbers traditionally use a line above a numeral (a vinculum) to multiply it by 1000, but the convention is not consistent and most modern uses just switch to Arabic numerals.