The best sex should last between seven and 13 minutes, and even three-minute sex is "adequate", a major survey of US experts has concluded.

But Australian sex therapists commenting on the new research say most men Down Under wanted it to last considerably longer while most women were "not bothered" if it was over with fast.

The sex study is the first to review what the experts believe is the ideal length of time to have penetrative sex, with the random sample of Americans and Canadians labelling seven to 13 minutes most "desirable".