Why is one gross equal to 144?

Answer 1

That's because that's how a gross is defined. The number 144 was chosen because it is a dozen dozens (12 x 12).

Answer 2

Oh, dude, one gross is equal to 144 because a gross is a unit of measurement that represents a dozen dozens. So, like, if you have 12 dozens, which is 12 x 12, you get 144. It's just a fancy way of saying a really big bunch of something.