About

Roman Numeral Converter turns numbers into Roman numerals and back, shows how each answer is built, and points out numerals that break the rules.

How the converter works

One small library does every conversion, both when the pages are built and in your browser as you type, so the answer printed on a page and the answer in the converter cannot disagree. A number is split into thousands, hundreds, tens and ones; each place is written with its own symbols; the parts are joined from largest to smallest.

Going the other way, the converter reads a numeral letter by letter and checks it against the standard rules: the seven symbols, at most three repeats, V, L and D never repeated, only the six subtractive pairs, and values that never rise except inside a pair. When a rule is broken it says which one, marks the letters involved, and suggests the standard form. If a numeral could mean more than one number, every reading is listed.

Numbers from 1 to 3999 use standard numerals. With the vinculum option, a bar over a letter multiplies it by 1000, which reaches 3,999,999.

Where the facts come from

The number pages mention where each numeral appears: Super Bowls, kings, queens and popes, films and games, Olympic Games, clock faces and Unicode. Every fact was checked by hand against its source, and each one links to it. Facts we could not confirm with confidence were left out. The current set was reviewed on October 4, 2026.

There are 24 number pages and 22 numeral pages so far. Pages are added in batches, and only numbers with enough verified material get a page of their own; every other number is in the chart and the converter.

What it does not do

It does not store what you type: conversion happens in your browser. It does not have accounts, and it does not guess silently. The full set of rules it applies is on theRoman numeral rules page.