Roman Numeral Converter
Two-way instant conversion between Roman numerals and decimal numbers with formula breakdowns.
Roman Numeral Chart
Complete Guide to Roman Numerals: Rules, Subtractive Notation & Conversion
Roman numerals originated in ancient Rome and remained the standard numbering system throughout Europe until the late Middle Ages. Today, Roman numerals are universally featured in clock faces, copyright dates, royal monarch titles, book chapter headers, and major sporting events.
The 4 Fundamental Rules of Roman Numerals
- 1. Additive Principle: When a smaller or equal numeral follows a larger numeral, values are added (e.g.,
VI = 5 + 1 = 6). - 2. Subtractive Principle: When a smaller numeral precedes a larger numeral, subtract its value (e.g.,
IV = 5 - 1 = 4,IX = 10 - 1 = 9). - 3. Repetition Limit: Symbols I, X, C, and M can never be repeated more than 3 times in a row.
- 4. Non-Repeating Symbols: Symbols V, L, and D are never repeated or used in subtractive notation.
Subtractive Pairs Reference
Only 6 specific subtractive pairs are valid in standardized Roman notation:
Key Roman Numeral Conversion Chart
| Arabic Number | Roman Numeral | Breakdown Expression | Common Usage |
|---|---|---|---|
| 10 | X | 10 | iPhone X, Decade |
| 50 | L | 50 | Super Bowl L |
| 100 | C | 100 (Centum) | Century |
| 500 | D | 500 | Historical Dates |
| 1000 | M | 1000 (Mille) | Millennium |
| 2026 | MMXXVI | 1000 + 1000 + 10 + 10 + 5 + 1 | Current Era Year |
Frequently Asked Questions (FAQ)
Is there a Roman numeral for zero (0)?
No, the classical Roman numeral system had no character for zero. The concept of zero as a placeholder was later introduced to the western world through the Hindu-Arabic numeral system. Medieval scholars occasionally used the Latin word nulla (meaning "none").
Why is 4 written as IIII instead of IV on many clock dials?
Traditional horology uses IIII for visual symmetry and aesthetic balance across the clock face, creating equal divisions of four Is (I, II, III, IIII), four Vs (V, VI, VII, VIII), and four Xs (IX, X, XI, XII).
What is the highest number you can write in standard Roman numerals?
In standard notation without using vinculos (over-bars for thousands), the maximum number is 3,999 (MMMCMXCIX).