3 months, 3 weeks and 3 days, is the Gestation Period of a pig. Gestation is the carrying of an embryo or fetus inside female viviparous animals. It is typical for mammals, but also occurs for some non-mammals. Mammals during pregnancy can have one or more gestations at the same time. In mammals such as pigs, pregnancy begins when a zygote (fertilized ovum) implants in the female's uterus and ends once the fetus leaves the uterus.
On the main article link above, are average and approximate gestation values ordered by number of days (note: human gestational age is counted from the last menstrual period; for other animals the counting method varies, so these figures could be 14 days off)