Roman numeral converter
Convert a whole number to a roman numeral, or a roman numeral back to a number. Runs entirely on your device, nothing is uploaded.
Roman numeral converter turns a whole number from 1 to 3999 into its roman form, or reads a roman numeral back into a number, based on what you type. Converting back also checks the numeral is written in its one canonical form, so IIII is refused with IV suggested. Numbers outside 1 to 3999 have no roman form.
Questions
What range of numbers does it support?
Whole numbers from 1 to 3999. Anything below 1 or above 3999 has no representation in standard roman numerals and is refused with "roman numerals here cover whole numbers 1 to 3999".
How does it know whether to convert to or from roman numerals?
From the shape of what you type: if the input matches a plain integer pattern, it converts to a roman numeral; otherwise it is parsed as a roman numeral and converted to a number.
What happens if I type a non-canonical roman numeral, like IIII?
It is refused. The tool converts your input to a number and then back to its own canonical roman form, and if that does not match exactly what you typed, it reports the input as not canonical and suggests the correct spelling, IV in that example.
Does it accept lowercase roman numerals?
Yes. Input is upper-cased and trimmed before being checked, so iv and IV are treated the same.
What characters are allowed in a roman numeral?
Only M, D, C, L, X, V and I. Anything else in the input is refused with a message naming exactly those seven allowed characters.