Roman Numeral Converter: Convert Between Roman and Arabic Numerals
Roman numerals have been used for millennia and still appear today on clock faces, movie copyright dates, book chapters, and sporting events like the Super Bowl. Our Roman Numeral Converter instantly converts between Roman numerals (I, V, X, L, C, D, M) and Arabic numerals (1, 2, 3...) and handles numbers up to 3,999 with proper subtractive notation. Use our Roman Numeral Converter to estimate your costs.
How Roman Numerals Work
The Roman numeral system uses seven symbols: I (1), V (5), X (10), L (50), C (100), D (500), and M (1,000). Numbers are formed by combining these symbols, with larger values generally placed before smaller ones to indicate addition. When a smaller value appears before a larger one, it indicates subtraction.
For example, VI = 5 + 1 = 6, but IV = 5 - 1 = 4. Similarly, XII = 10 + 1 + 1 = 12, and IX = 10 - 1 = 9. This subtractive notation prevents four identical symbols in a row (IIII becomes IV).
Using the Roman Numeral Converter
Enter a Roman numeral (like MMXXIV) or an Arabic number (like 2024). The converter instantly shows the equivalent in the other system. It validates input and shows the step-by-step breakdown: for Roman to Arabic, it adds the values of each symbol and applies subtractive rules; for Arabic to Roman, it breaks the number into thousands, hundreds, tens, and ones.
The calculator supports standard Roman numerals from 1 to 3,999. Larger numbers were historically indicated with a vinculum (bar above) multiplying the value by 1,000, but this is rarely used in modern contexts.
Conversion Rules
Additive Rule
When a symbol is placed after a larger or equal symbol, add its value. VI = 5 + 1 = 6. XIII = 10 + 1 + 1 + 1 = 13. LXXX = 50 + 10 + 10 + 10 = 80.
Subtractive Rule
When a symbol is placed before a larger symbol, subtract its value. Only powers of 10 (I, X, C) can be used subtractively, and only against the next two higher symbols. I before V or X (IV = 4, IX = 9). X before L or C (XL = 40, XC = 90). C before D or M (CD = 400, CM = 900).
Repetition Rule
A symbol can be repeated up to three times in a row. III = 3, XXX = 30, CCC = 300. Four in a row is not allowed — instead use subtractive notation.
Common Roman Numerals Reference
- 1 = I, 2 = II, 3 = III, 4 = IV, 5 = V
- 6 = VI, 7 = VII, 8 = VIII, 9 = IX, 10 = X
- 20 = XX, 30 = XXX, 40 = XL, 50 = L
- 60 = LX, 70 = LXX, 80 = LXXX, 90 = XC, 100 = C
- 500 = D, 900 = CM, 1,000 = M
- 2024 = MMXXIV (1,000 + 1,000 + 10 + 10 + 4)
- 1999 = MCMXCIX (1,000 + 900 + 90 + 9)
Where Roman Numerals Are Used Today
Clock faces often use IIII instead of IV for aesthetic symmetry. Movie copyright dates use Roman numerals (MMXXIV for 2024). Book chapters and volume numbers traditionally use Roman numerals. Monarchs and popes use Roman numerals (Elizabeth II, Pope Francis I). The Olympic Games and Super Bowl use Roman numerals (Super Bowl LVIII).
In outlines and lists, Roman numerals are used for main sections (I, II, III) with capital letters for subsections (A, B, C) and Arabic numerals for details (1, 2, 3).
Real-World Example
Convert the year 1984 to Roman numerals:
- Thousands: 1,000 = M
- Hundreds: 900 = CM
- Tens: 80 = LXXX
- Ones: 4 = IV
- Result: MCMLXXXIV
Convert MCMXLVII to Arabic: M(1,000) + CM(900) + XL(40) + VII(7) = 1,000 + 900 + 40 + 7 = 1,947.
Start Converting
Use our Roman Numeral Converter below to convert between Roman and Arabic numerals. Also check our Number Base Converter for other number system conversions and our Percentage Calculator for everyday math.
Reading Modern Years Quickly
Most everyday Roman numerals you encounter are copyright years, and they all follow the same pattern: convert thousands first, then hundreds, tens, and ones. The year 2024 is MMXXIV, 2025 is MMXXV, and 2026 is MMXXVI — each built from MM (2,000) plus the tens and ones, with 2027 following as MMXXVII.
For years with a four or nine in any position, the subtractive rule applies: 1990 is MCMXC (1,000 + 900 + 90) rather than MCCCCCCCCLXXXX. Once you can read M (1,000), CM (900), XC (90), and IX (9), any modern date decodes in seconds, which is exactly what the converter automates when you paste in a copyright line like MCMLXXXIV.
Related Calculators
Use our Roman Numeral Converter Guide together with related tools such as Area Calculator, Combination Calculator, Derivative Calculator to plan more accurately. Each calculator runs instantly in your browser with step-by-step guidance.
Written by the CalcMaster Pro Editorial Team — financial, health, and DIY tools reviewed for accuracy. All calculators run on standard, widely accepted formulas. Always confirm final numbers with a qualified professional for decisions that require official figures.