Both numbers are totally wrong. Because both should be closer to a quarter million, and not 200. Even one gram of sugar already has over 4000 calories.

But besides that, and this is probably your question: you only need a tiny amount of artificial sweetener, to get the same sweetness that you would get with sugar. For example Aspartam is about 200x as sweet as sugar, but it contains a very similar amount of energy. Sugar has ca. 16.8 kJ/g and Aspartam more like 17 kJ/g.

A gram of Splenda might be 10 times as sweet, and occupy 10 times as much volume, as a gram of brown sugar.