File & Format Converters · Free tool
Roman Numerals Converter
Convert between Arabic numbers (1–3999) and Roman numerals. Validates and rejects malformed forms like IIII.
Updated May 2026
Quick reference
- I = 1
- V = 5
- X = 10
- L = 50
- C = 100
- D = 500
- M = 1000
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What it does
Bidirectional Roman ↔ Arabic numeral conversion (1 to 3999). Validates input on both sides and round-trips so malformed forms like "IIII" or "VV" are rejected, not silently accepted. Useful for movie credits, book chapters, monarch ordinals, and Super Bowl numbers.
Embed this tool on your siteShow snippetHide
Paste this snippet into any page. Loads on-demand (lazy), no tracking scripts, and sized to most dashboards. Replace the height to fit your layout.
<iframe src="https://freetoolarena.com/embed/roman-numerals-converter" width="100%" height="720" frameborder="0" loading="lazy" title="Roman Numerals Converter" style="border:1px solid #e2e8f0;border-radius:12px;max-width:720px;"></iframe>How to use it
- Type a number into either field.
- The other field updates instantly.
- Invalid inputs (out of range, malformed) show an explanation.
Frequently asked questions
- Why only 1–3999?
- Classical Roman numerals don't have a standard form for zero or for 4000+. The system maxes at MMMCMXCIX (3999) without resorting to less-common overline notation. Years and chapters fall well within range.
- Why is IIII rejected?
- Standard subtractive form writes 4 as IV, 9 as IX, 40 as XL, etc. IIII shows up on clock faces but isn't standard Roman. The tool follows the strict form so converting back round-trips cleanly.
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