Roman numeral converter
Convert a number into Roman numerals or decipher a Roman inscription (monument, film credits, clock) in both directions.
Number → Roman numerals
Roman numerals → number
How it works
Roman numerals still appear regularly: the production date in a film's credits, the year engraved on a monument, a book chapter number, or the hour markers on certain clocks. This tool converts in both directions: enter a number to get its Roman form, or enter a Roman inscription to find out its exact value — handy for checking that you've correctly deciphered a date or for validating the spelling of a Roman numeral before using it.
Why is the conversion limited to 3999?
The classic Roman system (I, V, X, L, C, D, M) has no standard symbol beyond M (1000) that allows composing numbers unambiguously past 3999 (MMMCMXCIX). Extended conventions exist for very large numbers, but they aren't standardized; this tool therefore sticks to the classic range.
What happens if I enter an invalid Roman numeral?
The tool checks that every entered character is indeed part of the Roman alphabet (I, V, X, L, C, D, M) and displays a clear error otherwise. However, it doesn't check whether the order of the symbols matches a "canonical" Roman notation: it adds and subtracts values according to the standard rule (a smaller symbol placed before a larger one is subtracted), which covers the vast majority of real-world inscriptions.
Privacy: the conversion runs entirely in your browser via WebAssembly — your values are never transmitted to a server.