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.
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.
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.