You'll have to give us the recipe we can't guess what skinny soup is. 3 cups is 3 servings so my first question is, why not eat half and save half for another meal.
This is the 0 points cabbage soup from Weight Watchers. I am just wondering if I decide to eat just that for dinner and have, say 3 cups, will the points still be 0?
NUTRITION ESTIMATE
Per Cup: 61 Cal; 4 g Protein; 0 g Tot Fat; 0 g Sat Fat; 13 g Carb; 3 g Fiber
Looks like technically the soup isn't 0 points, but is 1 pt. The information above is from someone non-affiliated with WW, but calculated the nutritional.
So...assuming it is correct, you would triple all of the info except the fiber (caps out at 4), and 3 cups would be 3pts.