Roman Numeral Converter
Convert between decimal numbers and Roman numerals — instant bidirectional conversion
Decimal Number (1–3999)
Roman Numeral
Quick examples
Roman numeral reference ▸
| Symbol | Value |
|---|---|
| I | 1 |
| V | 5 |
| X | 10 |
| L | 50 |
| C | 100 |
| D | 500 |
| M | 1,000 |
Subtractive notation
| Symbol | Value | Rule |
|---|---|---|
| IV | 4 | 5 - 1 |
| IX | 9 | 10 - 1 |
| XL | 40 | 50 - 10 |
| XC | 90 | 100 - 10 |
| CD | 400 | 500 - 100 |
| CM | 900 | 1000 - 100 |
You’re formatting chapter numbers for a book, generating copyright year footers (MMXXVI), or parsing Roman numerals from an old API response. The rules for Roman numeral construction — subtractive notation, letter values, ordering — are simple but easy to get wrong. This converter handles both directions instantly.
Why This Tool
Mental Roman numeral conversion is error-prone for large numbers. Is 1994 MCMXCIV or MXMIV? (It’s MCMXCIV.) This tool converts in both directions — type a decimal number or a Roman numeral and get the other form immediately. It validates input and shows the breakdown of how each component maps.
Roman Numeral Basics
Roman numerals use seven symbols:
| Symbol | Value |
|---|---|
| I | 1 |
| V | 5 |
| X | 10 |
| L | 50 |
| C | 100 |
| D | 500 |
| M | 1000 |
Additive Rule
Symbols are generally written from largest to smallest, left to right, and their values are added: XVII = 10 + 5 + 1 + 1 = 17.
Subtractive Rule
When a smaller symbol precedes a larger one, subtract: IV = 5 − 1 = 4, XC = 100 − 10 = 90.
The six subtractive combinations:
| Combo | Value |
|---|---|
| IV | 4 |
| IX | 9 |
| XL | 40 |
| XC | 90 |
| CD | 400 |
| CM | 900 |
Conversion Algorithm
Decimal → Roman: Repeatedly subtract the largest possible value and append its symbol.
Example: 2024
- 2024 − 1000 = 1024 → M
- 1024 − 1000 = 24 → MM
- 24 − 10 = 14 → MMX
- 14 − 10 = 4 → MMXX
- 4 − 4 = 0 → MMXXIV
Result: MMXXIV
Common Year Conversions
| Year | Roman |
|---|---|
| 2026 | MMXXVI |
| 2025 | MMXXV |
| 2024 | MMXXIV |
| 2000 | MM |
| 1999 | MCMXCIX |
| 1990 | MCMXC |
Where Roman Numerals Are Used
- Copyright notices: © MMXXVI
- Book chapters and outlines: Chapter XIV
- Clock faces: Traditional clock dials use IIII for 4 (not IV)
- Movie sequels and events: Super Bowl LVIII
- Legal documents: Section III, Paragraph ii
- Academic outlines: I, II, III for major sections
Frequently Asked Questions
What is the largest Roman numeral? Standard notation goes up to 3,999 (MMMCMXCIX). For larger numbers, vinculum notation places a bar over a numeral to multiply by 1,000. This tool supports values beyond 3,999 using this extended notation.
Why is 4 written as IV instead of IIII? The subtractive rule (IV = 5 − 1 = 4) makes numerals shorter and avoids four consecutive identical symbols. However, clock faces traditionally use IIII for visual balance.
Is there a Roman numeral for zero? No. The Roman numeral system has no symbol for zero. It was developed before the concept of zero was adopted in Western mathematics.
Are lowercase Roman numerals valid? Yes. Lowercase (i, ii, iii, iv) is commonly used for sub-sections, page numbers in book prefaces, and footnotes. This tool accepts both cases.
Does this tool work offline? Yes. The conversion algorithm runs entirely in JavaScript in your browser with no network requests.