The size of the vagina is determined by hormones and genes and can vary in different times and conditions. When the vagina is relaxed, the vaginal walls collapse to each other and may seem loose. When a woman is ready for sex, the diameter of the vagina is not the same throughout sex. When a woman gives birth, the vagina stretches to many times its normal size to allow the baby to leave the mother's body.
Attribution: Straight Talk Foundation