To do this correctly, you need to look at what the markets for X are in a particular country or region.
I'm also appalled with two p's that the author is invoking the "Chinaman" sales fallacy. Once upon a time it was through that China had vast importing potential, for if you could get just 1% of its men to buy a wool suit, you'd be minting gold.
Of course, that ignores the minor detail of why anyone in China would desire a wool suit, let alone be able to pay for it.
Anytime you hear someone say "if we could get just XX% of this market", remember that each sale is made one at a time, and that those individual sales have got to make sense before you can get wild eyed with percentages and big numbers.