Roman Numeral Converter
Convert between Roman numerals and decimal numbers (1–3999) in both directions.
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Roman Numerals Guide
Roman numerals are a numeral system that originated in ancient Rome and remained the dominant number system in Europe until the late Middle Ages. They use letter combinations to represent values and are still used today for clock faces, movie copyright dates, Super Bowl editions, and chapter numbers.
The Seven Basic Symbols
I=1, V=5, X=10, L=50, C=100, D=500, M=1000. These seven symbols combine to represent all integers from 1 to 3999 in standard notation. V, L, and D cannot be repeated consecutively; I, X, C, and M can each be repeated up to three times.
The Subtractive Principle
When a smaller value precedes a larger one, subtract it instead of adding. Valid subtractive pairs: IV=4, IX=9, XL=40, XC=90, CD=400, CM=900. Only specific pairs are valid — IC (for 99) and VX (for 5) are not standard. This rule was fully standardized around the 9th century.
Reading Roman Numerals
Read left to right. If a symbol is followed by a smaller or equal symbol, add it. If followed by a larger symbol, subtract it. MCMXCIX: M(1000) + CM(900) + XC(90) + IX(9) = 1999. XLVII: XL(40) + V(5) + II(2) = 47.
Modern Uses
Super Bowl (LVII), Olympic Games, copyright years in films (MMXXIV for 2024), clock faces, outlines and lists (I, II, III…), monarch/pope names (Henry VIII, Pope John Paul II), and architectural inscriptions all use Roman numerals.
Quick Conversion Reference
| Arabic | Roman | Arabic | Roman |
|---|---|---|---|
| 1 | I | 50 | L |
| 4 | IV | 90 | XC |
| 9 | IX | 100 | C |
| 14 | XIV | 400 | CD |
| 40 | XL | 1000 | M |
| 49 | XLIX | 2024 | MMXXIV |
Frequently Asked Questions
I=1, V=5, X=10, L=50, C=100, D=500, M=1000. Combined: IV=4, IX=9, XL=40, XC=90, CD=400, CM=900.
2024 = MMXXIV. Breakdown: MM=2000, XX=20, IV=4.
MCMXCIX = M(1000) + CM(900) + XC(90) + IX(9) = 1999. This was commonly seen at the turn of the millennium.
The subtractive principle: I before V means 5−1=4. IIII was actually used historically (and appears on clock faces), but IV became the standardized form for cleaner writing.
3999 = MMMCMXCIX, since M can only repeat 3 times. Values over 3999 required a vinculum (bar over the letter) to multiply by 1000, but that's non-standard today.
2025 = MMXXV. Breakdown: MM = 2000, XX = 20, V = 5. Add them: 2000 + 20 + 5 = 2025.
The Roman numeral system developed for counting and commerce, not for positional arithmetic. Zero was not needed as a placeholder because the system used distinct symbols for each value group. The concept of zero as a number was developed separately in India and spread through Arabic mathematics.