Roman Numeral Converter

Convert Arabic numerals to Roman numerals and vice versa. Supports values from 1 to 3999.

How Roman Numeral Conversion Works

Roman numerals are an additive-subtractive numeral system developed in ancient Rome and still widely used today. This converter allows you to switch between Arabic and Roman numerals.

The Seven Base Symbols

The Roman system uses seven letters of the Latin alphabet: I (1), V (5), X (10), L (50), C (100), D (500), M (1000).

Composition Rules

Two fundamental rules govern Roman numeral composition:

Additive rule: when a smaller symbol follows a larger one, values are added. Example: VI = 5 + 1 = 6, XIII = 10 + 1 + 1 + 1 = 13.
Subtractive rule: when a smaller symbol precedes a larger one, it is subtracted. Example: IV = 5 - 1 = 4, XC = 100 - 10 = 90, CM = 1000 - 100 = 900.

The Six Subtractive Combinations

Only six subtractive combinations are valid: IV = 4, IX = 9, XL = 40, XC = 90, CD = 400, CM = 900.

The Repetition Rule

A symbol can be repeated at most three consecutive times (I, X, C, M). Symbols V, L, D are never repeated. That is why 4 is written IV and not IIII.

The Conversion Algorithm

The algorithm for converting an Arabic number to Roman is simple: start from the largest value (1000), repeatedly subtract the largest possible value from the number, add the corresponding symbol to the result string, and proceed to the next value until reaching zero.

Notable Examples

2026 = MMXXVI (current year)
1994 = MCMXCIV (classic example with subtractions)
3999 = MMMCMXCIX (largest number in the standard system)

Frequently Asked Questions

How do Roman numerals work?▼

Roman numerals use seven base symbols: I (1), V (5), X (10), L (50), C (100), D (500), M (1000). Numbers are formed by adding values when a smaller symbol follows a larger one (VI = 6) and subtracting when it precedes (IV = 4).

Why is the limit 3999?▼

In the standard Roman system, the largest representable number is 3999 (MMMCMXCIX), because there is no symbol for 5000. Romans used a line above the number (vinculum) to multiply by 1000, but this notation is not used in the modern standard system.

Where are Roman numerals still used?▼

Roman numerals are still used for: century numbering (XXI century), order of monarchs and popes (John XXIII), clock faces, book chapters, dates on monuments, event numbering (Olympics, Super Bowl), and class designations in some countries.