Roman numerals

Roman numerals appear on clocks, in years on buildings, in monarch names or chapter numbers. They are built from the letters I, V, X, L, C, D and M and follow fixed rules - such as subtraction, where IV stands for four and IX for nine. This tool converts both ways: you enter an ordinary number and get the Roman notation, or you enter Roman numerals and get the numeric value.

The tool detects automatically what you enter. For a Roman input it also checks that it is correctly formed: an invalid spelling like IIII or VV is honestly reported as an error instead of producing a wrong value. The supported range is one to 3999, the classic extent of Roman numerals without special marks for larger values.

The whole conversion runs entirely locally in your browser in pure JavaScript - your input is not uploaded, not stored, and no foreign library is loaded from a CDN. You can download the result as a text file or copy it straight out.

Specifications

In 3 steps

1. Paste a number or Roman numeral into the text field.
2. Click convert.
3. Read the result or download it as a text file.

Limitations: The classic range of 1 to 3999 is supported; larger numbers would need overline marks and are not covered. An invalidly formed Roman numeral leads to an honest error instead of a wrong value. Only whole numbers are converted.

FAQ

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