Roman Numeral Converter
Convert between Roman numerals and integers. Supports 1–3999.
Reference
Roman numerals are a numeral system developed in ancient Rome that uses seven letters — I (1), V (5), X (10), L (50), C (100), D (500), and M (1000) — to represent integers. The system uses additive notation for most values (III = 3, LX = 60) and subtractive notation for six specific combinations: IV (4), IX (9), XL (40), XC (90), CD (400), and CM (900). Only these six subtractive forms are standard — IIII is non-canonical even though it appears on some clock faces.
The standard range stops at 3,999 (MMMCMXCIX) because the system has no symbol for 5,000 or 10,000. Medieval scholars extended the range using an overline (vinculum) to multiply a numeral by 1,000, but this convention is not part of the modern ASCII system and is rarely used today. For numbers above 3,999, standard decimal notation is universally preferred.
Roman numerals remain in common use for specific purposes: Super Bowl numbering, film sequel titles (Rocky II, Star Wars Episode IV), chapter headings in formal documents, year labels on buildings and films, clock faces, and the names of monarchs and popes (King Charles III, Pope John Paul II). Their persistence in these contexts signals formality, tradition, or prestige rather than practical advantage over decimal notation.
Frequently Asked Questions
Why does the range stop at 3999?+
Standard Roman numerals use M for 1000. Three Ms in a row (MMM = 3000) plus CM (900) + XC (90) + IX (9) gives MMMCMXCIX = 3999. Going beyond 3999 requires special notation — an overline above a numeral multiplies it by 1000 — which is not part of the standard ASCII Roman numeral system and is rarely used today.
What is subtractive notation?+
Subtractive notation is the rule that a smaller numeral placed before a larger one means subtraction. For example, IV = 5 − 1 = 4, and XC = 100 − 10 = 90. Only six subtractive combinations are standard: IV (4), IX (9), XL (40), XC (90), CD (400), CM (900). Writing IIII instead of IV is technically additive notation, used on some clock faces but not accepted by this converter.
Where are Roman numerals still used today?+
Roman numerals appear in many modern contexts: movie sequel numbers (Rocky II, Star Wars Episode IV), Super Bowl numbering, clock faces, chapter numbers in books, year labels on buildings and films, outline numbering in academic documents, and the names of monarchs and popes (e.g. King Charles III, Pope John Paul II).
Why does the converter reject some Roman numeral strings?+
The converter validates input by converting the parsed integer back to canonical Roman numerals and comparing it to what you entered. This catches malformed strings like IIIII (should be V), VV (should be X), or IIX (non-standard). Only strings that match the canonical form produced by the integer→Roman conversion are accepted.
Related Tools
How to use
- Type an integer (1–3999) to see the Roman numeral equivalent.
- Type a Roman numeral (e.g. XIV, MMXXIV) to see the integer value.
- Both fields update instantly as you type.
- Only standard Roman numerals using subtractive notation are accepted.