Convert numbers to Roman numerals and back (1 to 3999) - locally in your browser, with no upload.
Running locally on your device ...
Running locally on your device ...
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Your files never left your device
No. Everything runs in your browser - your file never leaves your device. How this is verifiable
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.
| Input formats | Text input |
|---|---|
| Output format | TXT |
| Batch processing | No |
| Processing | Locally in your browser (JavaScript) |
| File upload | None |
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.
No. The conversion runs entirely locally in your browser; your input never leaves your device and is not stored.
One to 3999 - the classic extent of Roman numerals. Larger values require overline notations, which are deliberately not covered here.
An invalid spelling like IIII or VV is honestly reported as an error. The tool checks correctness by converting the result back.
Yes. A plain number is turned into Roman numerals, Roman numerals are turned into the numeric value - you do not need to switch anything.