Roman numeral converter
Convert between Roman and Arabic numbers, both ways.
Fill in the fields and the result will appear here automatically.
Converts Arabic integers to a chosen modern canonical Roman notation and back. The supported range 1–3999 limits thousands to three Ms and uses the subtractive pairs IV, IX, XL, XC, CD and CM. This is the tool’s convention, not the limit of every historical Roman notation: additive variants, overlines and other extensions are unsupported. Reverse conversion ignores case but requires the canonical spelling.
How it works
Formula and logic
Symbols are taken largest first; the subtractive pairs CM, CD, XC, XL, IX and IV keep the writing canonical.
Example
1994 is MCMXCIV: M + CM + XC + IV.
Fields and units
- Direction — list option
- Arabic number — unitless
- Roman numeral — unitless
How to use
- — Choose the direction.
- — Enter the number or the numeral.
- — Read the result.
Method and limitations
- Calculation method
- Formula and logic
- Limitation
- The supported range 1–3999 limits thousands to three Ms and uses the subtractive pairs IV, IX, XL, XC, CD and CM. This is the tool’s convention, not the limit of every historical Roman notation: additive variants, overlines and other extensions are unsupported.
FAQ
Why does the range stop at 3999?
This chosen canonical format allows at most three Ms and uses subtractive pairs. Other conventions can express larger values, such as additive MMMM for 4000. This calculator does not parse those extensions; 3999 is a limit of its format.
Why is IIII rejected?
IIII occurs on clock faces and can also mean 4. This tool chooses IV so the input matches its canonical encoder. Multiple spellings for one number do not inherently make decoding ambiguous; rejection enforces this chosen canonical form.
Is there a Roman zero?
No. The system has no symbol for zero and no negative numbers.
Are lowercase letters accepted?
Yes, the input is read case-insensitively and the answer is shown in capitals.