How Long Does The Average Female Orgasm Last?

Until it ends... I know, that's not much of an answer, but as all things involving people, it varies from person to person, and even varies with different partners, level of stimulation, level of her excitement at the moment... There are too many variables. It can go from a few seconds to (in the case of 'multiple' orgasms) a minute or more.

Length of orgasm is not nearly as important as quality of orgasm... So long as the female in question is enjoying herself, that should be sufficient...

Hope that helps, and you have a great day!