A single sperm is all that is needed, yet somehow nature felt that millions each and every time, JUST IN CASE, would be a better strategy. Personally, I think that was a very energy-wasteful choice on the part of biological evolution. But the point is that if you do not have any sperm capacity deficits (low sperm count, vasectomy, or castration), then any ejaculation has the ability to produce a zygote (fertilized egg) providing that an egg is present or will be in a few days (sperm can survive within the womb for a week or more, so always use protection).
