Roman Numeral Converter
Enter an Arabic number (1–3999) to get the Roman numeral, or enter a Roman numeral to decode it. Two-way conversion with instant results and validation. Runs entirely in your browser.
Convert ordinary integers to standard Roman numerals and Roman numerals back to integers. The supported integer range is 1 through 3999.
How to convert Roman numerals
- Enter an integer from 1 to 3999 to create a Roman numeral.
- Or enter a Roman numeral such as XIV to convert it back to a number.
- Copy either converted result with its copy button.
Roman notation and validation
Integer conversion uses the common subtractive forms IV, IX, XL, XC, CD, and CM.
Roman input is uppercased, parsed, and converted back to Roman form. Non-canonical strings are rejected when the round trip does not match.
Privacy and limitations
Roman numeral conversion runs entirely in your browser. The number or Roman numeral you enter is processed locally and is not intentionally uploaded by this tool.
Frequently asked questions
What numbers are supported?
Integers from 1 through 3999.
Can I type lowercase Roman numerals?
Yes.
Is IIII accepted for 4?
No. The validator expects IV.
Can it represent zero?
No.
Why is a Roman numeral rejected even if its letters are valid?
The tool also checks canonical ordering by converting the value back to Roman notation.