Granular Splenda in the box has 24 grams of carb per cup, or roughly 0.5 grams of carb per teaspoon or 1.5 grams of carb per tablespoon, 6 grams of carb per 1/4 cup, etc...
It's not the Splenda that actually has the carbs, it's the filler that they put in the box with the Splenda to give it the same volume cup for cup as sugar.