What is a Roman numeral converter?
Roman numerals build numbers from seven letters — I (1), V (5), X (10), L (50), C (100), D (500), M (1000) — and are still used on clocks, book chapters, movie copyright years and event editions. This Roman numeral converter turns Arabic numbers into Roman numerals and back, live: type in one field and the other updates. Everything runs locally in your browser.
How to use
- Type an integer from 1–3999 in the "Number" field and the Roman numeral appears on the right.
- Or type a Roman numeral (like MCMLXXXIV) and the number appears on the left.
- Out-of-range or invalid Roman numerals show an error.
Common use cases
- Read the copyright year at the end of a film (e.g. MMXXVI = 2026).
- Number chapters, appendices or outlines in Roman.
- Tattoos, logos and typographic design. Need other bases? Use the number base converter.
Why is 4 shown as IIII on clocks, not IV?
By the subtractive rule, 4 should be IV — yet countless clock faces carve it as IIII. That's not a typo but a clockmaking tradition: one common explanation is that IIII balances the dial visually against the VIII directly opposite it. So the IV this tool produces is the mathematically standard form, while IIII is an accepted special case on dials — both are "right", just for different contexts. What you should actually avoid is invented spellings: writing 9 as VIIII, or skipping ranks like XM for 990. The standard only lets I, X and C subtract one step up (IV, IX, XL, XC, CD, CM), and this converter only ever outputs that canonical form. For ordinary number bases, use the number base converter instead.
Why does it refuse anything above 3999?
Because classical notation has no letter for it. Type 4000 and the output field stays empty with the message ✗ Enter an integer from 1 to 3999. The reason is arithmetic: M is the largest letter there is, and there is no letter for 5000 to subtract from, so 4000 would have to be MMMM — four identical letters, exactly what the subtractive rule exists to avoid. The ceiling itself is MMMCMXCIX, and 1990 is MCMXC — a year that recent looks crowded because two subtractive pairs, CM and XC, stack up in it.