Roman Numerals Converter
Learn the seven Roman numeral symbols and the subtractive rules, then convert between numbers 1 to 3999 and Roman numerals, with examples like 444 and 1666.
Results
Roman
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Educational estimates · not financial advice · free, no signup
Formula / how it works
I=1, V=5, X=10, L=50, C=100, D=500, M=1000. Add symbols from largest to smallest. Subtract only with IV, IX, XL, XC, CD and CM. No symbol repeats more than three times in a row.
Detailed guide
What it is, how to use it, how to read the numbers, common mistakes, a worked example, formulas, and FAQs.
What this calculator is
Roman numerals use seven letters: I, V, X, L, C, D and M. Values are added from left to right, so VIII is 5 + 3 = 8, unless a smaller symbol sits before a larger one, in which case it is subtracted, so IX is 10 − 1 = 9. Only six such pairs are allowed in standard writing. This converter translates in both directions between Arabic numbers from 1 to 3999 and Roman numerals. It is a handy reference for the rules behind the answer: the largest number, why 4 is IV, and which sequences are invalid. For a quick answer in the same range with a different layout, the Roman numeral converter page gives the same results.
When to use / who it helps
- You are decoding a numeral on a building, clock or film credit.
- You want to write a number in the standard form.
- You are studying the rules of Roman numerals.
- You are labelling an outline, volume or event.
- You are teaching or learning the system.
How to use
Steps
- Choose whether to convert a number to Roman or the reverse.
- Enter a whole number from 1 to 3999, or a Roman numeral.
- Read the result.
- Break a number into thousands, hundreds, tens and units to check by hand.
- For a numeral, read from left to right and look for subtractive pairs.
- Do not use symbols in a non-standard order.
How to interpret results
- M is the largest basic symbol at 1,000.
- A symbol repeated three times is the maximum, such as XXX for 30.
- Subtractive pairs only use I, X and C as the smaller symbol.
- MMMCMXCIX is 3999, the upper limit.
- The system has no zero.
Common mistakes & gotchas
- Using IIII or VV.
- Subtracting from a symbol more than two steps larger, such as IC for 99.
- Writing numbers above 3999 with extra Ms.
- Reading IV as 6 (adding instead of subtracting).
- Using lowercase or non-Roman letters.
Worked example
Worked example — 444, 1666 and XCIV
- 444 = 400 + 40 + 4 = CD + XL + IV = CDXLIV.
- 1666 = M + DC + LX + VI = MDCLXVI, which happens to use each of the symbols M, D, C, L, X, V and I exactly once.
- Read XCIV: XC = 100 − 10 = 90 and IV = 5 − 1 = 4, so 94.
- 3999 = MMM + CM + XC + IX = MMMCMXCIX.
Result: 444 is CDXLIV, and XCIV is 94.
To load the form's own demo values, tap Try example above the Calculate button.
How to calculate / formula
I=1, V=5, X=10, L=50, C=100, D=500, M=1000. Add symbols from largest to smallest. Subtract only with IV, IX, XL, XC, CD and CM. No symbol repeats more than three times in a row.
Frequently asked questions
What are the Roman numeral symbols?
I = 1, V = 5, X = 10, L = 50, C = 100, D = 500, M = 1,000.
What is 1666 in Roman numerals?
MDCLXVI.
Why can't I write 99 as IC?
Subtraction is limited to specific pairs; 99 is XCIX.
What is the largest number I can write?
3999 in standard notation.
How do I read IV?
5 minus 1, which is 4.
Is there a Roman numeral for zero?
No.