Read the subtractive pairs
I before V or X subtracts one. X before L or C subtracts ten. C before D or M subtracts one hundred. Other symbols add their values. The breakdown follows the same pairs.
A worked example
944 becomes CMXLIV: CM is 900, XL is 40, and IV is 4. Together they add to 944.
Before you use the result
This tool accepts the standard forms from 1 through 3999. Zero, negative numbers, fractions, overlines and nonstandard forms such as IIX are not included.