Everything is "binary" so "sizes" of things on computers should be in "powers of 2."
The "power of 2" nearest to 1,000 (a kilo-something) is 1024 = 2x2x2x2x2x2x2x2x2x2. For in-line printing, that's sometimes written 2E10 "two to the tenth power." So to those who are "fussy," a KiloByte is 1,024 Bytes. This is the "traditional" size of a KiloByte.
Similarly, a Megabyte should be 1,024 KiloBytes, or 1,048,576 Bytes. And a GigaByte should be 1,024 MegaBytes, or 1,073,741,824 Bytes.
The terms are used very loosely, especially by the "ad-speaks." It is not uncommon for some one to refer to a "million bytes" as a MegaByte, and mostly it's not too much of a problem. The real problem is determining whether the person who uses "suspect conversion" is 1.) being sloppy just for convenience, 2.) is really ignorant, and doesn't know any better, or 3.) is a liar salesman you shouldn't believe anyway.