Roman Numeral Converter: Convert Between Roman and Decimal Numbers
Convert between Roman numerals and decimal numbers instantly. Learn Roman numeral rules, symbols (I, V, X, L, C, D, M), and practical use cases.
February 14, 2026
What Are Roman Numerals?
Roman numerals are a numeral system that originated in ancient Rome and remained the dominant way of writing numbers throughout Europe for nearly two thousand years. Despite being largely replaced by the Hindu-Arabic decimal system, Roman numerals continue to appear in many modern contexts. Our Roman Numeral Converter makes it easy to translate between Roman numerals and decimal numbers in either direction.
The Seven Roman Numeral Symbols
The Roman numeral system uses just seven symbols to represent all numbers:
- I = 1
- V = 5
- X = 10
- L = 50
- C = 100
- D = 500
- M = 1000
These symbols are combined according to specific rules to form any number from 1 to 3999 in standard notation.
Rules of Roman Numerals
Addition Rule
When a symbol of equal or lesser value follows a larger symbol, their values are added together. For example, VI equals 6 (5 + 1), XII equals 12 (10 + 1 + 1), and MDCLXVI equals 1666 (1000 + 500 + 100 + 50 + 10 + 5 + 1).
Subtraction Rule
When a symbol of lesser value precedes a larger symbol, the smaller value is subtracted from the larger. This is used to avoid writing four identical symbols in a row. For example, IV equals 4 (5 - 1), IX equals 9 (10 - 1), XL equals 40 (50 - 10), XC equals 90 (100 - 10), CD equals 400 (500 - 100), and CM equals 900 (1000 - 100).
Repetition Rule
A symbol can be repeated up to three times consecutively to multiply its value. For example, III equals 3 and XXX equals 30. However, V, L, and D are never repeated because doubling them would equal the next higher symbol.
Common Conversion Examples
Here are some frequently encountered Roman numerals and their decimal equivalents:
- XIV = 14
- XLII = 42
- XCIX = 99
- CCLVI = 256
- DCCXII = 712
- MCMXCIX = 1999
- MMXXVI = 2026
Where Are Roman Numerals Used Today?
Despite their age, Roman numerals remain surprisingly common in modern life:
- Clock and Watch Faces: Many traditional and luxury timepieces use Roman numerals on their dials, typically writing 4 as IIII rather than IV for aesthetic balance.
- Movie and Television: Copyright years in film and TV credits are often displayed in Roman numerals, such as MMXXVI for 2026.
- Outlines and Lists: Academic papers, legal documents, and book chapters frequently use Roman numerals for section numbering.
- Monarchs and Popes: Historical figures are distinguished by Roman numeral suffixes, like Henry VIII or Pope Benedict XVI.
- Super Bowl Numbering: The NFL's championship game uses Roman numerals for each edition.
- Architecture and Monuments: Dates on buildings, cornerstones, and monuments are often inscribed in Roman numerals.
How to Use the Roman Numeral Converter
Our tool supports bidirectional conversion. Enter a decimal number (1 to 3999) to get its Roman numeral equivalent, or enter a Roman numeral string to see its decimal value. The converter validates your input and provides instant results. It catches common errors like invalid symbol sequences and numbers outside the standard range.
A Brief History
The Roman numeral system evolved from Etruscan numerals and was standardized during the Roman Republic. While it served commerce, engineering, and governance for centuries, it was gradually replaced by the Hindu-Arabic system beginning in the 13th century. The positional notation and concept of zero made arithmetic far more practical, but Roman numerals endure as a cultural tradition that connects us to antiquity.