About Romanize
A precise, private tool for working with Roman numerals.
Romanize began with a simple worry: a Roman numeral copied wrong is permanent. People bring us the dates that matter most, the ones headed for a ring, a headstone, or their own skin, and those numbers deserve a tool that treats them as something to be set in stone rather than typed and forgotten.
So we built the quiet, exacting opposite of the cluttered converter. Every numeral is round-tripped for accuracy, rendered in the same inscriptional capitals Rome cut into marble, and computed entirely on your device. No accounts, no tracking, no ads. Just numerals, set in stone.
What this is
Romanize is a free converter and reference for Roman numerals. It turns numbers into numerals and numerals back into numbers, spells figures out in words, and documents every rule behind the system. Alongside the core converter there is a full chart, a live clock, a tattoo stencil generator and a page for individual numbers so you can link straight to the answer you need.
How it works
Every conversion runs in your browser using plain JavaScript. There is no server doing the maths, which means the tool is fast, works offline once loaded, and never sees what you type. The logic follows the standard rules for numerals from 1 to 3999, with a bracket notation for larger values where a bar would normally sit over a letter.
Why we built it
Most Roman numeral pages online are cluttered, slow, or stop at a single lookup. Romanize aims to be the opposite: quick to load, pleasant to read, and thorough enough that you rarely need a second tab. Accuracy matters here more than most places, because a numeral copied wrong can end up carved in stone or inked on skin.
How we check accuracy
Every conversion is generated by one small, well-tested function, never typed by hand, and then round-tripped: the numeral is converted back to a number and checked against the original. Malformed forms such as IIII, VV or IL are rejected, so you only ever see the canonical numeral. The rules we follow are the standard ones: the seven symbols I, V, X, L, C, D and M; additive order from largest to smallest; the six subtractive pairs (IV, IX, XL, XC, CD, CM); no symbol repeated more than three times; and V, L and D never repeated at all. Numbers above 3999 use the bracketed vinculum form. The same engine powers the converter, the chart, the per-number and per-numeral pages and the JSON API, so a fact on one page cannot disagree with another.
Sources for the history
The arithmetic is settled, but the historical notes on these pages (where a symbol came from, why there is no zero, why clocks show IIII) are drawn from standard reference works rather than invented. We cross-check claims against general references such as Encyclopaedia Britannica on Roman numerals, and we keep the wording cautious where the history itself is uncertain, for example the disputed origins of the symbols or the several overlapping explanations for the IIII on clock faces. Where a claim is a convention rather than a hard fact, we say so.
Accuracy and corrections
If you spot something that looks off, please tell us on the contact page. Reference pages carry a visible last-updated note so you know how current they are, and the machine-readable dates in the sitemap and structured data are kept in step with it.
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Last updated July 22, 2026. Reviewed for accuracy against the standard rules for Roman numerals.