The Bible gives several hints about the duration of the Flood, but it is difficult to determine exactly how long it lasted.
One verse says, “The waters prevailed upon the earth an hundred and fifty days” (Genesis 7:24). The Bible also uses Noah’s age as a measurement for the length of the Flood. It records that on the seventeenth day of the second month of Noah’s six hundredth year, the rains began to fall (Genesis 7:11-12). On the first day of the first month of his six hundred and first year, “the face of the ground was dry” (Genesis 8:13-14).
So the Flood must have lasted at least five months (150 days) and perhaps as many as nine or ten months. It would have taken the earth several months to dry out after such a massive flood.