Generally, pain is believed to happen when penetration goes beyond the comfort zone of the vaginal canal, which is usually 3 to 4 inches when not aroused and 5 to 7 inches when aroused.

Getting too deep depends on individual differences and level of arousal, but when a partner complains of a sharp or aching pain during penetration, that is a sign to do either of the following; slow down, change position, or stop going as deep.