Roman Numeral

Converting Between Numbers and Roman Numerals

A Roman numeral is a number written using combinations of the letters I, V, X, L, C, D, and M, each standing for a fixed value (1, 5, 10, 50, 100, 500, and 1,000). Enter a whole number to see its Roman numeral spelling, or enter a Roman numeral to see the number it represents.

Roman numerals are built by combining symbols and adding their values together, largest to smallest, left to right — for example, MCMXCIV is M (1,000) + CM (900) + XC (90) + IV (4) = 1,994. The Romans themselves used a looser system over the centuries, but the version taught and used today follows a consistent, standardized convention (the one this calculator uses).

The Formula

1. Number to Roman: starting from the largest value symbol (M = 1,000) down to the smallest (I = 1), repeatedly subtract that symbol’s value from the number and append the symbol, as many times as it fits, before moving to the next smaller symbol.
2. Roman to number: scan the letters and add each symbol’s value — except when a smaller-value symbol appears immediately before a larger one, which means “subtract” instead (as in IV, IX, XL, XC, CD, and CM).
3. Standard Roman numerals never repeat the same symbol more than three times in a row — a four-in-a-row situation (like 4, or “IIII”) is instead written as a subtractive pair (“IV”) using the next symbol up.

Worked Example

Converting the number 1,994:

1. 1,994 contains one 1,000 → M
2. What’s left (994) contains one 900 (the subtractive pair for “one hundred less than a thousand”) → CM
3. What’s left (94) contains one 90 → XC
4. What’s left (4) is the subtractive pair for “one less than five” → IV
5. Put it all together: MCMXCIV

Key Factors to Consider

• Standard Roman numerals have no symbol for zero and no way to represent negative numbers. The Roman numeral system was designed for counting positive whole quantities — this is why this calculator’s own valid input range starts at 1, unlike the Hindu-Arabic (modern) number system used everywhere else on this site.
• Roman numerals are still widely used today for specific, traditional purposes rather than everyday counting. Clock and watch faces, movie/copyright year stamps in credits, Super Bowl numbering, and naming monarchs or popes (like Elizabeth II) are all common places Roman numerals persist — almost always for a stylistic or traditional reason rather than a practical arithmetic one.
• The standardized subtractive-pair convention (IV instead of IIII) is a relatively later refinement, not how Romans always wrote numbers historically. Ancient Roman inscriptions sometimes show both forms, and some clock faces still use “IIII” instead of “IV” for four purely by tradition — this calculator follows the modern, standardized convention taught today, not every historical variant.
• Roman numerals become impractical for arithmetic compared to the modern positional number system, which is exactly why they were eventually replaced for everyday calculation. There’s no simple Roman-numeral equivalent to long addition or multiplication the way the Hindu-Arabic system allows — this is a major reason the positional decimal system became the global standard for actual computation.

Common Mistakes

• Writing a symbol four or more times in a row instead of using the subtractive pair. “IIII” for 4 or “VIIII” for 9 aren’t standard modern usage — the correct forms are “IV” and “IX”, using the next symbol up in a subtractive pair.
• Placing a subtractive pair’s smaller symbol before the wrong larger symbol. Only specific subtractive pairs are valid (IV, IX, XL, XC, CD, CM) — something like “IL” for 49 isn’t a real Roman numeral, since I can only subtract from V or X, never from L.
• Assuming any number can be converted. Standard Roman numerals only cover 1 through 3,999 — there’s no standard way to write zero, negative numbers, or anything 4,000 and above.

Useful to Know

• Curious about a number’s prime factors instead of its Roman numeral form? Prime Factorization Calculator breaks a number down into its prime factors.
• Working with very large or very small numbers? Scientific Notation Calculator converts a number to and from scientific notation.
• Need to convert a number between binary, hexadecimal, or another base? Number Base Converter converts a number between any two number bases.