Roman Numeral Converter
Convert between Roman numerals and Arabic numbers.
Overview
The Roman Numeral Converter translates between Arabic numbers (1, 2, 3...) and Roman numerals (I, II, III...) in either direction. It handles the standard subtractive form (IV for 4, IX for 9, XL for 40) up to numbers in the thousands.
It is built for students learning ancient numeral systems, designers picking chapter or movement numbering, copyright-year readers staring at confusing film credits and anyone preparing documents with Roman page numbers.
How it works
The standard Roman numeral system uses M = 1000, D = 500, C = 100, L = 50, X = 10, V = 5 and I = 1. Numbers are formed by additive combination, with the subtractive rule allowing one smaller numeral immediately before a larger one to mean "subtract." Only IV, IX, XL, XC, CD and CM are valid subtractive pairs.
To convert from Arabic to Roman, the algorithm greedily emits the largest symbol that fits and subtracts it from the remaining value, repeating until zero. To go the other way, scan left to right: if the current symbol's value is less than the next, subtract; otherwise add.
Examples
1990 → MCMXC
2024 → MMXXIV
MCMLXVII → 1967
XLIX → 49
FAQ
What's the largest number Romans wrote?
The classical system tops out around 3999 (MMMCMXCIX) because four M's in a row is non-standard. Larger numbers used overlines to multiply by 1000.
Why isn't 4 written as IIII?
Subtractive notation became standard in the Middle Ages — IV is shorter and the modern convention. Some clocks still use IIII for visual balance.
Is zero a Roman numeral?
No, Romans had no symbol for zero. Their numeral system handles positive integers only.
Can I have a fractional Roman numeral?
The system supports unciae (twelfths) using dots and a symbol for half, but that's a curiosity rather than a modern need. The converter handles integers only.
Why are some Roman numerals on movie credits unusual?
Movie copyright years often use a slightly stylised long form to make the date less obvious to viewers. They still follow the same rules.