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.

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.