Roman Numeral Converter

What Roman numerals are, and where you still see them

Roman numerals are a way of writing numbers with seven letters from the Latin alphabet: I, V, X, L, C, D and M. There is no place value as in our everyday decimal notation; you string symbols together and add or subtract their values. That makes arithmetic awkward, but the notation survives wherever a number is meant to look formal or ceremonial: clock faces, copyright years at the end of film credits, chapter and volume numbers, cornerstones and building plaques, regnal numbers such as Elizabeth II, and the numbering of recurring events such as the Super Bowl or the Summer Olympic Games. Type a number on the left and the converter writes the Roman form on the right, together with the exact pieces it was built from, so you can use it as a quick lookup or as a way to learn the rules.

The seven symbols

How the rules work: adding and subtracting

When symbols run from larger to smaller, you add them: VIII is 5 + 1 + 1 + 1 = 8 and XXVI is 10 + 10 + 5 + 1 = 26. When a smaller symbol sits directly in front of a larger one, you subtract it: IV is 5 − 1 = 4. The standard form allows exactly six such pairs.

Three conventions complete the standard form. A symbol may be repeated at most three times in a row, so 4 is IV, not IIII. The symbols V, L and D are never repeated, so 10 is X, not VV. And subtraction is allowed only in the six pairs above: I may precede V and X, X may precede L and C, and C may precede D and M. That is why 99 is XCIX (90 + 9) and not IC, and 49 is XLIX (40 + 9) and not IL. This converter reads whatever you type into a number, converts that number back to the standard form, and compares the two strings. If they differ, the input was not written in standard form and you get an explanation instead of a silent answer.

Place-value table

Roman numerals are really the decimal system in disguise: each decimal digit gets its own chunk, and the chunks are joined from the thousands down to the ones. Pick one entry from each column and put them side by side and you can write any number from 1 to 3999. The table below is generated at build time by the same conversion function the tool uses.

To write 1994, split it into 1000 + 900 + 90 + 4 and take M, CM, XC and IV from the columns: MCMXCIV. The "Breakdown" line in the tool prints exactly this sequence.

Worked examples, checked by calculation

Example 1: reading MCMXCIV. M (1000) + CM (900) + XC (90) + IV (4) = 1994.

Example 2: writing 2024. 2000 is MM, 20 is XX and 4 is IV, so the year is MMXXIV. A film that ends its credits with MMXXIV was made in 2024.

Example 3: why 49 is XLIX. 49 = 40 + 9 = XL + IX. Writing IL would mean "50 minus 1", which skips a decimal place, and the standard form does not allow that kind of shortcut.

A quick way to read a numeral

Scan from left to right and ask one question at each letter: is it smaller than the letter to its right? If yes, subtract it; if not, add it. For MCMXCIV that gives +1000, then C is smaller than the M after it so −100, +1000, then X is smaller than the C after it so −10, +100, then I is smaller than the V after it so −1, and finally +5, which totals 1994. With practice you stop doing this letter by letter and instead read in decimal chunks of thousands, hundreds, tens and ones. Writing works the same way in reverse: peel off the largest decimal chunk, find it in the table, and move to the next one.

Non-standard spellings and how this tool treats them

Real-world inscriptions are sometimes looser than the textbook. The table lists spellings people often type, the number a simple left-to-right reading gives them, and the verdict here.

Note that "IIX" for 8 and "XM" for 990 are not accepted either: they look plausible but have no place in the standard rules, and their literal readings (10 and 990) are not what the writer meant. If you are decoding an old inscription that uses such a form, treat the converter's rejection as a hint that the carver followed a local habit, not as a sign that your input is wrong.

Why the range stops at 3999

M is the largest symbol and can be repeated three times, so the largest standard number is MMMCMXCIX, which is 3999. Larger numbers were written with a bar over a symbol to multiply it by 1000, but a bar does not fit into plain text, so this tool does not support it. There is also no Roman symbol for zero and no way to write negatives or fractions in the standard system, so input of 0, negative numbers and decimals is rejected with a message. Across all 3999 supported numbers the Roman form averages 7.5 characters, and the longest is 3888 at 15 characters.

Common mistakes and misunderstandings

• "IIII is simply wrong." In the standard form 4 is IV, yet many clock faces deliberately show IIII. That is a long-standing dial convention, not an arithmetic error, so the converter still reports IIII as non-standard.
• Using IC for 99. I can only come before V and X. Write XC (90) followed by IX (9): XCIX.
• Thinking position changes value. A letter always has the same value; only a smaller letter directly before a larger one is subtracted.
• Lowercase. Lowercase i, ii, iii is common for outline numbering and front matter page numbers. The converter uppercases whatever you type, so lowercase is accepted.
• Unicode Roman numeral characters. Single characters such as Ⅳ or Ⅻ exist for typesetting, but plain letters I, V and X are safer for search, copy and paste, and screen readers.
• Zero, negatives and fractions. They cannot be written in the standard system; the tool shows a message instead of a result.

Getting the most out of the result

1. For a copyright line or a title card, enter the year and press "Copy Roman numeral" to paste it elsewhere.
2. For numbered sections, check the breakdown to confirm the chunks are right before you commit to a long list.
3. To decode a date on a building or the front matter of a book, type it into the Roman numeral box. If you get a "not valid" message, compare it with the table above; an unusual spelling is more likely than a bad reading.
4. For arithmetic, convert to Arabic numbers, calculate, then convert back; the notation itself is not designed for adding or multiplying.

The converter runs entirely in your browser. Nothing you type is sent anywhere.

Frequently Asked Questions

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