Convert Roman Numeral to Hex
Convert Roman numerals to hex (and back) with strict 1-3999 validation. Batch TSV output. Free, offline, client-side, instant, secure.
Bidirectional Roman-to-hex converter with strict canonical validation. Rejects bad forms like IIII, IC, VV instead of silently producing wrong numbers. Batch mode emits a TSV table (Roman / Decimal / Hex) ready to paste into a spreadsheet. Range capped at the standard Roman maximum of 3999.
How to Use Convert Roman Numeral to Hex
- Type or paste your Roman numeral. Use standard letters I, V, X, L, C, D, M (case is normalized to uppercase). For batch conversion, enter one numeral per line or separate with commas -
IV, X, MCMXCworks the same as one-per-line. - Watch the live validator. The tool checks canonical form via regex -
IIII,VV,IC, and similar non-standard patterns are rejected with a specific error explaining what's wrong (not just "invalid format"). Standard subtractive formsIV/IX/XL/XC/CD/CMare the only allowed pairings. - Choose hex formatting. Two toggles: Uppercase (default on -
0x7C6vs0x7c6) and "0x" prefix (default on - strip for languages that don't need it like assembly without a leading sigil). - Read the result. Single inputs show the hex value plus the decimal underneath in the stats line. Batch inputs show a TSV table (Roman / Decimal / Hex) - paste straight into Excel or Google Sheets and it parses into 3 columns.
- Use Swap for reverse. The Swap button flips direction to Hex → Roman. Input becomes
0x7C6/7C6/#7C6(any prefix accepted), output becomesMCMXC. Same 1-3999 range applies - hex above0xF9Fis rejected because Roman has no symbol for 4000+. - Copy or Download. Copy puts the visible output text on your clipboard. Download saves
roman-hex.txtfor single conversions orroman-hex.tsvfor batches (TSV-friendly extension makes it open in spreadsheet apps automatically). - Stats line tracks everything. Shows direction, count parsed, ok vs error counts, and the sum of all decimal values (useful as a sanity check when batch-converting a known total).
Frequently Asked Questions
Does it actually reject IC, IIII, and other non-standard forms?
Yes – that’s the main feature. The validator uses regex ^M{0,3}(CM|CD|D?C{0,3})(XC|XL|L?X{0,3})(IX|IV|V?I{0,3})$ which only matches canonical Roman. IC would naively decode to 99 by right-to-left subtraction, but it’s not standard Roman (which is XCIX) so this tool rejects it with the error “Only IV/IX/XL/XC/CD/CM are valid subtractive pairs”. Many converters silently accept IC and produce 99 – this one doesn’t.
What’s the maximum Roman numeral?
3999, written MMMCMXCIX (hex 0xF9F). Standard Roman has no symbol for 4000 – historically the Romans used a bar over the letter (vinculum) to multiply by 1000, but that requires special characters and isn’t part of standard ASCII Roman input. MMMM is rejected with a specific error pointing to the 3999 cap.
Can I go from hex back to Roman?
Yes – click the Swap button. Direction flips and the input accepts hex with any common prefix: 0x7C6, 7C6, #7C6 all parse the same. Output becomes the canonical Roman form, generated by greedy subtraction from the symbol table. Same 1-3999 range applies in both directions.
How does batch mode format the output?
Tab-separated values (TSV) with a header row: RomantDecimaltHex for forward conversion or HextDecimaltRoman for reverse. Each input line becomes one row; failures get the row INPUTtERRORt<message> so you can spot which entries failed without losing alignment. Download as .tsv opens directly in spreadsheets.
Do I have to put one per line, or can I use commas?
Both work. The batch splitter accepts newlines AND commas as separators in the same input. So IVnXnMCMXC, IV, X, MCMXC, and even IV,XnMCMXC all produce three results. Whitespace around entries is trimmed.
Why no zero or negative numbers?
The Roman numeral system has no symbol for zero (the concept of zero arrived in Europe centuries after Rome’s writing system) and no notation for negatives. The tool returns a specific error “Hex value 0 has no Roman equivalent (Romans had no zero)” for hex 0 and rejects negative decimals upstream. If you need zero for programming purposes, you’ll need a different representation.
What’s the difference between uppercase and lowercase hex?
Visual only – both are mathematically identical. 0x7C6 and 0x7c6 mean the same value (1990). Some style guides prefer one over the other; C and Rust commonly use lowercase, assembly often uses uppercase. Toggle the box to match your codebase convention.
Why include the “0x” prefix toggle?
Different contexts expect different prefixes. C, JavaScript, Python, and Rust use 0x. CSS uses #. Some assemblers use $ or a trailing h. Some contexts (database hex columns, file content) use no prefix at all. The toggle controls whether 0x appears so you can paste straight into your target.
Is my input uploaded anywhere?
No. Roman numeral parsing, validation, hex encoding, and TSV generation all run in your browser. Open DevTools → Network and confirm zero requests fire – even when you Convert or Download. Safe for sensitive numerical data, custom serial numbers, or anything you’d rather not send to a third-party converter.
Does it work offline?
Yes. Total bundle is about 18 KB. Load once, disconnect, keep using. Roman numeral conversion is a one-shot read of the page – no API calls, no fonts to fetch, no analytics. Useful for quick conversions on planes or during outages.