According to the Bible, eight people were on the Ark. The Book of Genesis identifies Noah, his wife, Noah's three sons, and the three sons' wives as the human occupants who survived the Flood.
Genesis 7:13 describes Noah entering the Ark with Shem, Ham, and Japheth, along with their wives. Counting the four men and four women gives a total of eight people. The biblical account also says that animals were brought aboard, but the number of animals is described in different ways in Genesis, which is why traditions and interpretations sometimes vary on that detail.
The number eight is specific to the biblical narrative. Later Jewish, Christian, and Islamic traditions retell aspects of Noah's story, but details can differ between scriptures and commentaries. Another common mix-up is counting only Noah's immediate family without including the wives; the wives are the reason the traditional biblical total is eight rather than four.