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Roman numeral converter
Turn Arabic numbers into Roman numerals or read them back. Covers the standard 1–3999 range with the subtractive rule, and rejects malformed numerals.
Input
Roman numeral
ConvertedType a number to see its Roman numeral.
Roman numerals combine seven letters — I, V, X, L, C, D, M — using addition and a subtractive rule (IV = 4, IX = 9). The standard system spans 1 to 3999; larger values historically used an overline to multiply by a thousand, which this tool doesn't cover.
A free Roman numeral converter that translates Arabic integers to Roman numerals and reads them back in both directions. Covers the standard range of 1 to 3999 using the subtractive notation rule (IV, IX, XL, etc.) and rejects values outside that range or numerals that violate the standard form.
How to use the Roman numeral converter
- Type an integer (1–3999) to convert it to Roman numerals.
- Type a Roman numeral string to convert it back to a number.
- The converter detects which direction to go automatically.
- Click the result to copy it.
The subtractive rule explained
Standard Roman numerals use seven letters: I (1), V (5), X (10), L (50), C (100), D (500), M (1000). To avoid four-in-a-row repetition, smaller values placed before larger ones are subtracted: IV = 4, IX = 9, XL = 40, XC = 90, CD = 400, CM = 900. Only these six combinations are valid subtractive pairs — other combinations such as IC or VX are not standard and are rejected.
Frequently asked questions
What is the largest number the Roman numeral converter handles?
3999 (MMMCMXCIX). Standard Roman numerals have no symbol for 4000 or above without using a bar (vinculum), which most systems omit.
Why is 4 written as IV and not IIII?
The subtractive rule was adopted to reduce repetition. IV places a smaller value before a larger one, indicating subtraction: 5 minus 1 equals 4.
Is this converter two-way?
Yes. Enter a number (e.g. 2024) to get MMXXIV, or enter a Roman numeral (e.g. MMXXIV) to get 2024.
What happens with invalid input?
Out-of-range integers and non-standard numeral strings are flagged with an error message rather than returning a wrong answer.