About Numerus
A clean, fast reference for Roman numerals: convert both ways, browse complete charts, and copy any modern year for a tattoo or an anniversary.
Written and checked by Jamey Weber, who maintains Numerus at FusionStudios. Last reviewed 5 August 2026. Every numeral on this page is produced by the same conversion logic the converter uses, which is covered by an automated test over all 3,999 values. See how we check this.
What this site is
Numerus does one thing well: Roman numerals. The two-way converter handles every standard value from 1 (I) to 3999 (MMMCMXCIX). Around it sit printable charts, dedicated pages for popular numbers and modern years, a date generator for tattoo designs, a tattoo guide, and a free JSON API for developers.
How the conversions work
Every conversion follows the standard rules of the numeral system, including the subtractive forms IV, IX, XL, XC, CD and CM. The maths runs entirely in your browser, so results are instant and nothing you type is sent to a server. The same rules power the converter, the charts and the API, so every part of the site always agrees.
Who maintains this
Numerus is written and maintained by Jamey Weber, a Dutch web developer and the person behind FusionStudios, a web studio that builds and runs a small group of free reference tools. He writes the guide pages, checks the per-number and per-year copy, and answers anything that comes in through the contact form. His other work is on jameyweber.com.
Corrections are the fastest thing to get his attention. If you find a numeral that is wrong, tell us and we will fix it and record it on this page. We do not publish a personal email address, because the form reaches the same person without collecting a mailbox that gets scraped. If you need a named contact for a citation or a licence question, ask through the form and you will get one.
How we verify
The rule set is the standard modern one: seven symbols (I, V, X, L, C, D, M), additive composition from largest to smallest, and exactly six subtractive pairs (IV, IX, XL, XC, CD, CM). Only I, X and C are ever subtracted, and only from the next one or two steps up. I, X, C and M repeat at most three times; V, L and D never repeat and are never subtracted. The range is 1 to 3999, because above that the standard notation needs a vinculum, an overline that multiplies a symbol by a thousand.
That rule set is implemented once, in a single conversion module, and every part of the site reads it: the converter, the charts, the number and year pages, the date generator and the JSON API. It is covered by an automated test suite that runs on every build and checks all 3,999 values in both directions, verifies that converting a number to a numeral and back returns the original number, and rejects the invalid forms people commonly try (IIII, VV, IC, IL, XD). The build fails if any of that breaks, so a wrong numeral cannot reach the site through a code change.
Editorial copy is a separate matter and gets checked by hand. Each guide page carries a visible last-reviewed date that only moves when somebody has actually read the page through. On 5 August 2026 we removed a usage line from the number pages that claimed any value up to 3999 appears in monarch and pope names. It was true for the first two dozen numbers and false for the rest, and it should never have been published.
Free, no sign up
Everything here is free to use, print and embed, with no account required. See the privacy page for how the site handles data, including any third-party ads or analytics. If you run a website, you can embed the converter with one line of HTML.