The Roman Numeral Converter is a simple but highly useful tool for converting between standard Arabic numerals and Roman numeral notation. You can enter any number and instantly see its Roman numeral equivalent, or enter a Roman numeral string and convert it back to a decimal number. Roman numerals are still in active use today across many contexts: clock faces, book chapter numbering, movie sequels, copyright years on films and television shows, architectural cornerstones, and formal documents. Students encounter Roman numerals in history and classical studies courses, while designers frequently use them for stylistic purposes. The converter handles the full standard Roman numeral range, properly applying subtractive notation rules (such as IV for 4 and IX for 9). The tool works entirely in your browser with no data storage or uploads. For complete results, Number Base Converter can convert numbers between binary, decimal, hex, and octal, Percentage Calculator can calculate percentage values and changes, and Binary ↔ Text can convert between binary and readable text.
Roman numerals follow a specific additive and subtractive notation system that trips up many people. The symbols I (1), V (5), X (10), L (50), C (100), D (500), and M (1000) are combined according to strict rules. When a smaller value appears before a larger value, it is subtracted: IV = 4, IX = 9, XL = 40, XC = 90, CD = 400, CM = 900. When a smaller value appears after a larger value, it is added: VI = 6, XI = 11, LX = 60. No symbol may be repeated more than three times consecutively in standard notation. This is why 4 is written as IV rather than IIII, though clock faces often use IIII for aesthetic balance. For large numbers, the modern convention allows M to be repeated: 2024 is written as MMXXIV. In classical Latin inscriptions, numbers above 3999 were sometimes indicated with a bar over a numeral (vinculum) to multiply it by 1000, but this is rarely needed in modern use. This converter also helps with checking the validity of Roman numeral strings, making it useful for writers, editors, and designers who need to verify that a number is correctly represented before publication.