Roman Numeral Converter

Convert between decimal numbers and Roman numerals

Roman numerals have been used for over two millennia and remain widely encountered today — on clock faces, in film and book titles, at the Super Bowl, in legal documents, and on monuments. This converter works in both directions: enter a decimal number to get its Roman numeral equivalent, or type Roman numerals to convert them back to decimal.

The Roman numeral system

Roman numerals use seven Latin letters as symbols: I (1), V (5), X (10), L (50), C (100), D (500), and M (1000). Numbers are formed by combining these symbols following two main rules:

Additive notation: Symbols are placed from highest to lowest and their values are added. III = 1+1+1 = 3. VIII = 5+1+1+1 = 8. XIII = 10+3 = 13.

Subtractive notation: When a smaller value symbol appears before a larger one, it is subtracted. This avoids sequences of four repeated symbols. The subtractive pairs are: IV = 4 (not IIII), IX = 9 (not VIIII), XL = 40, XC = 90, CD = 400, CM = 900.

Complete examples

• MMXXIV = 2000+20+4 = 2024 (the year 2024)
• XLII = 40+2 = 42
• CDXCIX = 400+90+9 = 499
• MCMXCIX = 1000+900+90+9 = 1999
• MMMDCCCLXXXVIII = 3888 (the longest standard Roman numeral)

Where Roman numerals appear today

Clocks and watches: Many traditional clock faces use Roman numerals for hours. Note that IV is sometimes written as IIII on clocks for visual symmetry.

Film and television: Production years of films and TV shows are often displayed in Roman numerals in end credits. Film sequels frequently use them: Rocky IV, Star Wars Episode IV.

Sports: The Super Bowl has been numbered with Roman numerals since Super Bowl V. The Olympics also use Roman numerals for their numbered games.

Monarchy and papacy: Rulers with the same name are distinguished by ordinals in Roman numerals: Elizabeth II, Pope John XXIII, Henry VIII.

Outlines and lists: Formal outlines (I. II. III. A. B. C. i. ii. iii.) use Roman numerals for major section numbers.

Architecture and monuments: Year numbers on cornerstones, monuments, and public buildings are traditionally carved in Roman numerals.

A note on non-standard forms

Not every Roman numeral you encounter follows the strict subtractive rules this converter uses. Historically, Romans themselves were not always consistent, and you will still see IIII instead of IV on some clock faces purely for visual balance opposite VIII, or additive-only forms in older inscriptions. This tool follows the standard modern convention — the one taught in schools and used in publishing, film credits and formal documents — which always prefers the shortest, subtractive form. If you type a non-standard variant such as IIII, treat any unexpected result as a sign that the input was not in standard form rather than an error in the conversion itself.

Limitations of Roman numerals

Roman numerals have no symbol for zero, no way to represent fractions, and no straightforward arithmetic — multiplying two Roman numerals by hand is laborious. This is why the system was gradually replaced by the Hindu-Arabic positional system (the digits 0–9) for calculation purposes.

How to use the converter

Type a decimal number into the first field to see its Roman numeral form appear instantly, or type Roman numerals into the second field to convert them back to a decimal number. Both directions update live as you type, so you can go back and forth freely — enter 1999, see MCMXCIX appear, then edit it slightly and watch the decimal value change to match. The converter accepts standard subtractive-notation Roman numerals, which cover every whole number from 1 up to 3,999, the traditional practical limit of the classical system.

Converting decimal to Roman, step by step

The conversion works by repeatedly matching the largest possible Roman value against what remains of the number, subtracting it, and moving on. For 1994: the largest value that fits is 1000 (M), leaving 994; then 900 fits (CM), leaving 94; then 90 fits (XC), leaving 4; then 4 fits (IV), leaving 0. Reading off the symbols in order gives MCMXCIV. This greedy, largest-first approach always produces the correct standard form because the Roman system was designed so that no smaller combination of symbols can represent the same value more compactly.

Converting Roman to decimal, step by step

Going the other way, the converter reads the Roman numeral from left to right and adds each symbol's value, except when a symbol is immediately followed by a larger one, in which case it is subtracted instead. For MCMXCIV: M (1000) is followed by C, which is smaller, so add 1000; C (100) is followed by M, which is larger, so subtract 100; M (1000) is added; X (10) is followed by C, larger, so subtract 10; C (100) is added; I (1) is followed by V, larger, so subtract 1; V (5) is added. Summing 1000 − 100 + 1000 − 10 + 100 − 1 + 5 gives 1994, matching the original number exactly.

Why there is no year zero and no Roman zero

One quirk worth knowing is that the Roman numeral system has no symbol for zero at all — the concept had not been formalised when the system was developed, and Roman numerals were designed purely for counting and recording quantities, not for the kind of positional arithmetic that a zero enables. This is also why the historical calendar jumps directly from 1 BC to AD 1 with no year zero in between, a quirk that still occasionally causes confusion when calculating the exact span between ancient dates.

Private and instant

The conversion runs entirely in your browser in both directions, so results appear the instant you type and no numbers you enter are ever uploaded, logged or shared. It works offline once the page has loaded.