How to use the Roman numeral converter
- Choose Number → Roman numeral when you have an ordinary whole number, or Roman numeral → Number when you have letters to decode.
- Enter a value. Numbers must be between 1 and 3999. Roman input may be uppercase or lowercase, but it must use the seven symbols I, V, X, L, C, D, and M.
- Select Convert. The result card shows the converted value and the canonical Roman spelling. Use Copy result when you need the plain result in another document.
- If the input is rejected, keep the value visible and correct the indicated problem. The converter does not silently reinterpret a nonstandard numeral.
How standard Roman numerals work
Roman numerals represent values with seven symbols: I is 1, V is 5, X is 10, L is 50, C is 100, D is 500, and M is 1000. Most symbols are written from larger to smaller and added. For example, VIII is 5 + 1 + 1 + 1, while MD is 1000 + 500.
Modern standard notation uses six subtractive pairs to avoid four repeated symbols: IV is 4, IX is 9, XL is 40, XC is 90, CD is 400, and CM is 900. The smaller symbol is subtracted only in those pairs. That is why 49 is XLIX, not IL, and 99 is XCIX, not IC.
For number-to-Roman conversion, the calculator repeatedly takes the largest available standard token, starting with M and including subtractive tokens such as CM. For Roman-to-number conversion, it first reads the value and then converts that number back to its canonical spelling. The input is accepted only when the spelling matches, which catches invalid repetition, ordering, and subtraction without guessing.
The range stops at 3999 because this page uses ordinary letters without overlines or extended symbols. In that system, 3999 is MMMCMXCIX. Roman numerals do not include a standard positional zero, so zero, negative values, decimals, and fractions are outside this converter.
Worked examples
1994 → MCMXCIV
Split 1994 into 1000 + 900 + 90 + 4. Those parts are M + CM + XC + IV, so the standard result is MCMXCIV. Converting MCMXCIV back produces 1994.
49 → XLIX
Forty is XL and nine is IX. Joining the two place-value groups gives XLIX. IL may look shorter, but I cannot subtract from L in standard notation, so IL is rejected.
Limits and common errors
- Only whole numbers from 1 to 3999 are supported. There is no zero result and no extended overline notation for 4000 or more.
- Only canonical modern forms are accepted. Historical inscriptions, clock-face IIII, medieval variants, and Unicode single-character numerals such as Ⅻ are not normalized here.
- I, X, C, and M may repeat at most three times in their normal positions. V, L, and D do not repeat. The converter rejects forms such as IIII, VV, and MCMC.
- Lowercase ASCII input is accepted and changed to uppercase. Spaces between symbols, punctuation, dates containing separators, and complete sentences are not parsed.
- The tool converts one value at a time. It does not interpret outlines, monarch names, copyright dates, or arithmetic expressions automatically.
Frequently asked questions
Why is 4 shown as IV instead of IIII?
IV is the standard subtractive form used by this converter. Some clock faces use IIII by tradition, but that display convention is outside strict modern notation.
What is the largest supported Roman numeral?
MMMCMXCIX, which equals 3999. Larger systems need an additional convention such as an overline, so they are deliberately excluded.
Can I enter lowercase letters?
Yes. Input such as mcmxciv is normalized to MCMXCIV before validation and converts to 1994.
Why is IC rejected for 99?
Only I before V or X is subtractive. Write 99 by place value: XC for 90 followed by IX for 9, giving XCIX.
Does the converter send my value anywhere?
No. Conversion and validation run in your browser tab, and no typed value is added to analytics events.