The average length of the external clitoris, composed of the glans plus the external descending portion of the clitoral body (palpable under the hood up to the mons) is about 1.6-2.9 cm (unfortunately the research on clitorises is so bad there is an absurd amount of variation in reported averages). Consider that the aroused clitoris is engorged and call it 1.9-2.2 cm for simplicity. If you consider the average erect penis 13 cm, then that is only 6–7 times the length. So theoretically based on this logic, men should take the basic penile stroke and divide by 6–7.