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How to use
Convert standard integers from 1 to 3999 to Roman numerals and back. The converter uses I, V, X, L, C, D and M with standard subtractive notation and strictly validates Roman input instead of accepting any letter sequence that happens to sum to a number.
- Enter an integer from 1 to 3999 or a Roman numeral.
- Use standard Roman symbols without spaces inside the numeral.
- Calculate to display both equivalent forms.
How it is calculated
Example
Example: 2026 converts to MMXXVI. MCMXCIX converts to 1999 because CM = 900, XC = 90 and IX = 9.
Important notes
This tool is limited to the common standard Roman range through 3999. Historical and modern extensions for larger values use overlines or other conventions that are not included here. Zero, negative numbers and fractions are unsupported.
Worked examples and interpreting results
Roman numerals use fixed-value symbols and specific subtractive pairs. IV means 4 rather than 6, while VI means 6. The table shows each numeral’s value, not its character count.
| Case | Calculation | Result |
|---|---|---|
| Numeral IV | V − I = 5 − 1 | 4 |
| Numeral XLII | (L − X) + I + I = 40 + 2 | 42 |
How to check the result
Use standard subtractive pairs such as IV, IX and XL: 49 is XLIX rather than IL. This notation does not supply a standard numeral for zero or fractions.
Frequently asked questions
Why is 4 IV instead of IIII?
Modern standard notation uses subtractive IV, although historical variants such as IIII exist on some clocks.
Will IIX be accepted as 8?
No. Standard 8 is VIII, so non-canonical IIX is rejected.
Why stop at 3999?
Standard notation with these symbols and no extended overline convention normally ends at MMMCMXCIX.