Roman Numeral Converter numeral

What this tool does

Roman numerals combine seven symbols: I for 1, V for 5, X for 10, L for 50, C for 100, D for 500, and M for 1000. The basic rule is to list symbols from largest to smallest and add them, with subtractive notation used to avoid repeating a symbol four times, which is why four is written IV rather than IIII.

Subtractive notation is restricted. I may precede only V and X, X only L and C, and C only D and M, which is why 99 is XCIX rather than IC. This tool follows those standard rules and rejects non-standard input by converting the parsed number back and checking that it matches the original string.

The supported range is 1 to 3999. Values of 4000 and above require an overline to indicate multiplication by a thousand, which plain text cannot express, so most tools stop at 3999.

When to use it

Use it to read Roman page numbers in a book or document, to decode a year on a clock face or building, to convert film series or event numbering, or to produce numerals for a design mockup.

Input and output examples

Notes and limitations

Zero and negative numbers cannot be expressed, because the Roman system has no concept of zero. Forms such as IIII, though sometimes seen in practice, violate the standard rules and are rejected here; the clock-face convention of writing IIII for four is an aesthetic exception. If you need to sort or calculate with Roman numerals, convert them to numbers first: sorting the strings directly puts IX before V and produces nonsense.

Frequently asked questions