How the chart is built
Britannica summarises the rule: a symbol after one of equal or greater value adds, and a symbol before one of greater value subtracts. Standard notation uses six subtractive pairs — IV (4), IX (9), XL (40), XC (90), CD (400) and CM (900) — and never repeats a symbol more than three times, so 4 is IV rather than IIII. Every value on this page was generated by the same strict converter used in the Roman numeral converter.
The longest numeral up to 100 is 88, LXXXVIII. Because M may appear only three times, MMMCMXCIX (3,999) is the largest number in standard form; larger values historically used a bar over the numeral to multiply by 1,000. To write a year or a full date in Roman numerals, use the converter’s date box.