Roman Numeral Converter
Convert numbers to Roman numerals, or Roman numerals back to numbers, instantly inside your browser.
How do Roman numerals work?
Roman numerals represent numbers using combinations of seven letters — I (1), V (5), X (10), L (50), C (100), D (500), and M (1000) — added together, with a smaller numeral placed before a larger one meaning subtraction instead (like IV for 4, or IX for 9). This tool converts in both directions, from a whole number to its Roman numeral form and back again.
GuideHow to use it
How the conversion works
Converting to Roman numerals repeatedly subtracts the largest possible numeral value (including subtractive pairs like CM for 900) from the number, appending each symbol as it's used, until nothing remains. Converting from Roman numerals reads the letters left to right, adding each value unless a smaller value comes immediately before a larger one, in which case it's subtracted instead. Numbers above 3999 aren't supported, since standard Roman numerals have no symbol larger than M (1000) without using overline notation.
Why it helpsFeatures & benefits
Why this runs entirely in your browser
The conversion runs in JavaScript locally in the tab, which means it keeps working offline once the page has loaded and nothing entered here is ever sent to a server.
Common uses
Reading a copyright year or movie release date written in Roman numerals, formatting a chapter or section number, or working through a homework problem on number systems.
Frequently asked questions
A few things people usually want to know before trusting the numbers.
3999 (MMMCMXCIX), since standard Roman numerals don't have a symbol for 5000 or higher without special overline notation.
Modern Roman numeral convention uses subtractive notation for four of the nine "awkward" digits (4 and 9 within each place value) — a smaller numeral before a larger one means subtraction, so IV means 5 - 1 = 4.
No — Roman numeral input is automatically converted to uppercase before being parsed, so lowercase letters work fine.
Not every combination of letters is a valid Roman numeral — this tool checks that the parsed number converts back to exactly the same numeral before accepting it as valid.
No. All conversion happens locally in your browser. Nothing typed here is sent to a server, stored, or shared.