This is a perfect illustration of why one should cook by weight and not, as in the Anglo-Saxon world, by volume.
1 cup of fluid heavy whipping cream (37% fat) weighs 238 grams (yields 6.64 carbs). 1 cup of the same heavy cream, whipped weighs 119.5 grams (yields 3.334 carbs).
Therefore, once whipped, cream doubles in volume but if you cooked by weight, you would be able to weigh exactly that cream, whipped or otherwise, and multiply each gram by exactly .02789958159 carbs…