Would a tsp be a good way to measure the capacity of a milk carton explain

In my opinion, I would not. Most milk cartons are half-gallon or 1.89 liters. One liter is around 200 teaspoons, and so if you measured by teaspoons, your answer would be around 400, specifically, 383.4511 teaspoons.

No it would not because a teaspoon is very small and can not practically tell you how much is in it now a graduated cylinder would because it is practical for a carton of milk and it can also tell you how much is in it.