Roman Numerals Converter
Convert between Roman numerals and Arabic (standard) numbers. Handles values from 1 to 3,999.
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How to use this calculator
Roman numerals use additive and subtractive notation. IV=4, IX=9, XL=40, XC=90, CD=400, CM=900.
- 1
Enter an Arabic number (1–3,999) to convert to Roman numerals.
- 2
The result shows the Roman numeral and a breakdown of each symbol.
- 3
Roman numerals above 3,999 require non-standard notation.
Frequently asked questions
Does this convert Roman numerals back to numbers?
No. Despite the page description, the form has a single field for an Arabic number and returns the Roman numeral, plus a symbol-by-symbol breakdown. To read a Roman numeral, add the values of the symbols left to right, subtracting any symbol that stands before a larger one. In MCMXCIV that gives 1000 + (1000 − 100) + (100 − 10) + (5 − 1) = 1994.
What is the largest number it can convert?
3,999, which is MMMCMXCIX. Standard notation only repeats a symbol up to three times, and there is no standard symbol above M, so 4,000 would need four M’s. Entering 4,000 or more returns an error asking for a value from 1 to 3,999.
Can I convert zero or negative numbers?
No. Roman numerals have no symbol for zero and no negatives, so 0 and anything below 1 are rejected. The field label mentions "0 to skip", but there is no second input; 0 simply produces the error message.
What happens if I type a decimal like 2024.9?
The decimal part is cut off, not rounded. 2024.9 is treated as 2024 and returns MMXXIV, and the Arabic Number line shows 2024 so you can see what was converted. Fractions are not supported.
Which subtractive pairs does it use?
Exactly six: IV (4), IX (9), XL (40), XC (90), CD (400) and CM (900). So 49 is XLIX rather than IL, and 1994 is MCMXCIV. Shortcuts like IC for 99 or VL for 45 are not produced, because they fall outside the standard rules.
Why does the breakdown list the same symbol more than once?
It shows each letter in the output with its value, in order. For 3888 (MMMDCCCLXXXVIII) the list has fifteen entries because the number is written with fifteen letters. Subtractive pairs also appear as separate letters: IV is shown as I=1, V=5, so read those two together as 5 − 1.
Does it ever produce variants such as IIII for 4?
No. Output is always the standard subtractive form, so 4 is IV and 9 is IX. The converter has no setting for older or alternative spellings.
Roman numerals converter — write 1 to 3,999 in Roman notation
How the conversion works
The converter takes the largest value from the list 1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4, 1 that still fits, writes its symbol, subtracts it, and repeats. Because the list includes the six subtractive pairs, it never writes four of the same letter in a row, and it always produces the standard form. It runs on whole numbers from 1 to 3,999; the page converts only from numbers to numerals.
| Symbol | Value | Pair | Value |
|---|---|---|---|
| I | 1 | IV | 4 |
| V | 5 | IX | 9 |
| X | 10 | XL | 40 |
| L | 50 | XC | 90 |
| C | 100 | CD | 400 |
| D | 500 | CM | 900 |
| M | 1000 | — | — |
Worked examples
These outputs come straight from the calculator. Notice how each result is built by greedy subtraction.
| Number | Roman numeral | How it is built |
|---|---|---|
| 49 | XLIX | XL (40) + IX (9) |
| 1994 | MCMXCIV | M + CM (900) + XC (90) + IV (4) |
| 2024 | MMXXIV | MM + XX + IV |
| 3888 | MMMDCCCLXXXVIII | MMM + D + CCC + LXXX + VIII |
| 3999 | MMMCMXCIX | MMM + CM + XC + IX |
Reading a numeral by hand
Scan from left to right and add each value, unless a symbol is smaller than the one after it, in which case subtract it. Take MCMXCIV: M is 1000, then C is smaller than M so CM is 900, then X is smaller than C so XC is 90, and finally I is smaller than V so IV is 4. Total 1994. Use that check on any output from the converter to confirm that it round-trips.
The longest and the limit cases
Among numbers up to 3,999, 3888 produces the longest numeral, MMMDCCCLXXXVIII, with fifteen symbols, because every digit position uses the maximum repetition of its symbols. The upper limit of 3,999 follows from the rule that M can appear at most three times. Anything bigger, such as 4,000, is rejected with an error rather than written in a non-standard way.
Typing tips
Enter plain digits without commas. A decimal is truncated, so 2024.9 becomes 2024 (MMXXIV). Leaving the field empty is read as 0 and returns the out-of-range error. Letters are not accepted because the field is numeric, which is why this page cannot be used to decode a numeral you have found on a building or a book. For that, do the left-to-right addition described above, then enter the number you get here to confirm that the converter writes it back the same way.
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