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Roman Numeral Converter
Enter a number from 1 to 3999 to get its Roman numeral, or enter a Roman numeral such as MCMXCIV to get the number. Non-standard forms are flagged with the correct spelling.
The seven symbols and what they are worth
Roman numerals are built from seven letters: I = 1, V = 5, X = 10, L = 50, C = 100, D = 500 and M = 1000. Values are normally added from left to right, so XVI is 10 + 5 + 1 = 16. There is no symbol for zero and no place-value column, which is why very large numbers become unwieldy.
This converter handles 1 to 3999, the range that the standard seven symbols can write without extra conventions such as an overbar for multiplying by a thousand.
The subtractive rule
To avoid writing four of the same symbol in a row, a smaller symbol placed before a larger one is subtracted. Only six pairs are standard: IV (4), IX (9), XL (40), XC (90), CD (400) and CM (900). So 1994 is M (1000) + CM (900) + XC (90) + IV (4), written MCMXCIV.
| Symbol before | Can precede | Examples |
|---|---|---|
| I | V, X | IV = 4, IX = 9 |
| X | L, C | XL = 40, XC = 90 |
| C | D, M | CD = 400, CM = 900 |
V, L and D are never used subtractively, and a symbol is never subtracted from something more than ten times larger, so IC for 99 is not standard; the correct form is XCIX.
How the conversion works
To write a number, the tool works greedily down a table of thirteen values from 1000 to 1, taking the largest value that fits and subtracting it until nothing is left. For 1994 that takes 1000, then 900, then 90, then 4.
To read a numeral, it scans left to right, subtracting a symbol when the next one is larger and adding it otherwise. As a check, it writes the result back in standard form and compares it with what you typed. If they differ, the input is flagged and the standard spelling is shown, so IIII, VX or IC are caught rather than silently accepted.
Variants you may see in the wild
Historical and decorative uses are looser than the modern standard. Clock faces often show 4 as IIII, and some old inscriptions use forms like XXC for 80. These are legitimate in context, but they are not accepted here because the tool follows one consistent rule set.
Roman numerals still appear in film and book copyright years, outline numbering, monarch and pope names, chapter headings and the Super Bowl. For years, convert each part separately, thousands first: 1987 is M, CM, LXXXVII, so MCMLXXXVII. Lowercase is also used for page numbers in a book's front matter, and the converter accepts any letter case.
Worked example
Write the year 2024 as a Roman numeral: two thousands, two tens and four, giving MMXXIV.
Inputs
| Number or Roman numeral | 2024 |
|---|
Result
2024 written as a Roman numeral.
| Number | 2024 |
|---|---|
| Roman numeral | MMXXIV |
| Breakdown | M = 1000 + M = 1000 + X = 10 + X = 10 + IV = 4 |
- Uses the standard subtractive forms IV, IX, XL, XC, CD and CM. Repeats are limited to three in a row.
Accuracy note: Results use standard double-precision arithmetic, so very large or very small values may be rounded. Check important results by another method.
Frequently asked questions
How do I write 2024 in Roman numerals?
Split it into 2000, 20 and 4: MM for 2000, XX for 20 and IV for 4. Joined together, 2024 is MMXXIV.
What is the largest number I can write in Roman numerals?
With the standard seven symbols the largest is 3999, written MMMCMXCIX. Larger numbers need an overbar over a symbol to multiply it by one thousand.
Why is 4 written IV and not IIII?
The subtractive convention shortens four repeats into one smaller symbol before a larger one. IIII still appears on some clock faces as a traditional style, but IV is the standard form.
Is there a Roman numeral for zero?
No. The Roman system had no symbol for zero, and the word nulla was occasionally used in writing. This converter therefore starts at 1.
Why does the tool reject some numerals I typed?
Strings like IC or VX add up to a value but break the standard rules. The tool shows the correct standard form so you can see how it should be written.
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References and sources
- Gullberg, J. Mathematics: From the Birth of Numbers (1997), chapter on numeral systems.