Roman Numeral Converter — Number ↔ Roman, Free Online
Convert between Roman numerals and Arabic numbers. Supports 1 to 3999 with strict canonical form (no IIII). Live validation, uppercase/lowercase output.
Roman Numeral Converter — Convert Numbers Both Ways
Convert between Arabic numbers (1, 2, 3…) and Roman numerals (I, II, III…) in either direction. The tool validates Roman numerals strictly — only canonical forms are accepted (so “IIII” is rejected; the correct form is “IV”). Works for values from 1 to 3999, the standard range of classical Roman numerals.
Roman numeral symbols
| Symbol | Value |
|---|---|
| I | 1 |
| V | 5 |
| X | 10 |
| L | 50 |
| C | 100 |
| D | 500 |
| M | 1000 |
Subtractive notation
Roman numerals use subtraction for certain combinations:
- IV = 4 (5 – 1), not IIII
- IX = 9 (10 – 1), not VIIII
- XL = 40 (50 – 10)
- XC = 90 (100 – 10)
- CD = 400 (500 – 100)
- CM = 900 (1000 – 100)
Examples
- 2024 = MMXXIV
- 1999 = MCMXCIX (NOT MIM)
- 3999 = MMMCMXCIX (the maximum)
- 1776 = MDCCLXXVI
- 2000 = MM
Why no zero?
The Roman numeral system has no symbol for zero — that concept was introduced to Europe later via Indian/Arabic mathematics. Roman numbers start at I (1).
Why max 3999?
In standard form, you can have at most three Ms in a row (3000). To express 4000+, Romans used a horizontal bar above letters to multiply by 1000, but this is not standard typography. This tool sticks to the strict 1-3999 range.
Common uses
- Movie copyright years (MMXXIV = 2024)
- Book chapter numbers (Chapter IV)
- Outline numbering (I., II., III., IV.)
- Monarch and pope titles (Louis XIV, Pope Francis I)
- Historical date conversion
- Educational quizzes
Privacy
Everything runs in your browser. Your numbers are never uploaded.
Step by step
- Choose the direction: 123 → CXXIII or CXXIII → 123.
- Type the number or the Roman numeral. The input is checked instantly.
- Pick uppercase or lowercase and copy the result.
- Use the swap button to reverse the conversion direction.
Frequently asked questions
Why only up to 3999?
Classical Roman numerals have no symbol for 5000. Up to 3999, every number can be written in the usual form (MMMCMXCIX).
Why is 4 written IV and not IIII?
The tool uses the canonical subtractive notation. Four identical symbols in a row are avoided, so 4 is IV and 9 is IX.
Where do Roman numerals appear?
On clocks and dials, in dates on buildings, in chapter numbers, in the names of kings and in anniversaries.