Convert numbers to Roman numerals and back — just type either one.
Instant and offline in your browser.
How do you convert numbers to Roman numerals?
Roman numerals use I=1, V=5, X=10, L=50, C=100, D=500 and M=1000, with subtractive pairs such as IV=4, IX=9, XL=40 and CM=900. Standard numerals run from 1 to 3999. For example, 2026 becomes MMXXVI, and MCMLXXXIV converts back to 1984. Malformed numerals like IIII or VX are rejected.
Understanding your result
Standard Roman numerals run from 1 to 3999. The converter validates input so malformed numerals like “IIII” or “VX” are rejected.
Formula and method
Roman numerals use I=1, V=5, X=10, L=50, C=100, D=500 and M=1000, with subtractive pairs such as IV=4, IX=9, XL=40 and CM=900.
Assumptions and limitations
Standard Roman numerals cover 1 to 3999 only, so the tool cannot represent zero, negatives, fractions or numbers of 4000 and above. It follows strict standard notation and rejects malformed input such as IIII or VX rather than guessing at an intended value.
Worked example
2026 becomes MMXXVI; MCMLXXXIV becomes 1984.
How to use this tool
- Type a number between 1 and 3999, or a Roman numeral.
- Press Convert to see the result instantly.
About the Roman Numeral Converter
The Roman Numeral Converter turns ordinary numbers into Roman numerals and decodes Roman numerals back into numbers, automatically detecting which direction you need.
Who should use this tool
History and Latin students decoding dates on monuments, writers formatting chapter and clock numbers, and anyone reading film copyright years or building numbering who wants to convert between ordinary numbers and Roman numerals in either direction.
Benefits
- Converts both ways and detects the direction automatically
- Validates input and rejects malformed numerals
- Applies correct subtractive pairs like IV, IX and CM
- Works instantly in your browser with no sign-up
Practical use cases
- Reading the copyright year at the end of a film
- Deciphering a Roman numeral date carved on a building
- Numbering book chapters or outline sections correctly
- Checking a clock face or monument inscription
Frequently asked questions
Why is the maximum 3999?
Standard Roman numerals only go up to 3999 (MMMCMXCIX); larger numbers need a bar notation that isn’t part of the everyday system.
How does subtractive notation work in Roman numerals?
When a smaller symbol sits before a larger one, it is subtracted rather than added. So IV is 5 minus 1, giving 4, and CM is 1000 minus 100, giving 900. The valid subtractive pairs are IV, IX, XL, XC, CD and CM; the tool applies these automatically.
Why is IIII rejected as invalid?
Standard notation never repeats a symbol four times in a row. The number 4 is written IV using subtraction, not IIII. The tool follows this convention strictly, so it flags IIII and other non-standard forms as invalid rather than converting them.