Roman Numeral Converter
Enter a number from 1 to 3999 or a Roman numeral like MMXXVI and get the other form instantly. Invalid numerals are explained rather than guessed.
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How to use Roman Numeral Converter
- Type a number between 1 and 3999, or a Roman numeral using I, V, X, L, C, D and M.
- The converted value appears straight away.
- Press Copy, or tap an example to see common conversions.
- If you see an error, read the hint and correct the input.
How Roman numerals work
Roman numerals use seven letters: I is 1, V is 5, X is 10, L is 50, C is 100, D is 500 and M is 1000. Values are normally added from left to right, so XVI is 10 + 5 + 1 = 16. When a smaller symbol is placed before a larger one, it is subtracted instead: IV is 4 and XC is 90.
Only I, X and C can be used for subtraction, and only against the next two larger symbols. That is why 49 is XLIX and not IL, and why 99 is XCIX and not IC.
Where you still see them
- Clock faces, building cornerstones and monuments.
- Chapter numbers, outlines and book front matter.
- Names of monarchs, popes and events such as Super Bowl editions.
- Copyright years at the end of film and television credits.
- Tattoos, anniversaries and decorative designs.
Conversion rules used here
To convert a number, the tool takes the largest Roman value that fits, writes its symbol, subtracts it, and repeats. To convert a numeral back, it first checks the whole string against the pattern of the standard form, then adds the values. Anything outside that pattern is reported as invalid rather than silently converted.
Historical writing sometimes uses variants, such as IIII or VIIII, and different centuries used different habits. If you are reading an old inscription, the strict result here may differ from how the original was written. Everything runs in your browser and nothing is stored or sent.
Some quick patterns make mental conversion easier. Write the thousands first, then the hundreds, tens and ones, converting each digit on its own: 1994 is 1000 (M), 900 (CM), 90 (XC) and 4 (IV), giving MCMXCIV. Going the other way, scan from the left and subtract whenever a smaller symbol precedes a larger one. For years, remember that 2000 is MM, so 2026 is MMXXVI, and the pattern continues cleanly until 3999.
Why use this roman numeral converter tool
- Both directions. The tool detects whether you typed digits or letters and converts accordingly.
- Strict validation. Forms like IIII, VX or IC are rejected with an explanation, since they are not standard.
- Case-insensitive. Type mcmxcix or MCMXCIX; both work.
- Quick examples. One-tap examples such as 1994 and 2026 show how subtractive notation works.
Frequently asked questions
Why does the converter stop at 3999?
Standard Roman numerals use M for 1000 and do not repeat a symbol more than three times, so the largest number that can be written in the usual way is MMMCMXCIX, which is 3999. Larger values need extended notation such as a bar over a letter, which is not part of the standard set.
Why is IIII marked as invalid?
Strict modern usage writes four as IV. IIII does appear on some clock faces and in old inscriptions, but this converter follows the standard rule that limits repeats and uses subtraction for 4, 9, 40, 90, 400 and 900.
Is there a Roman numeral for zero?
No. The Roman system had no symbol for zero as a number, so the tool starts at 1.
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