In the biblical Book of Genesis, how many days and nights did the rain of Noah's Flood fall?

In the biblical Book of Genesis, the rain of Noah's Flood fell for 40 days and 40 nights.

Genesis describes the rain beginning after Noah, his family, and the animals entered the ark. The repeated number 40 is a major biblical time period, also appearing in stories involving Moses and the Israelites. In the Flood narrative, however, the rain itself is distinguished from the longer period during which the waters remained powerful over the earth.

A common mix-up is to say that the entire Flood lasted only 40 days. Genesis also says that the waters prevailed for 150 days, and the complete sequence from the beginning of the rain until the ground was dry is much longer. The 40-day figure specifically describes the downpour.

The story appears in Genesis chapters 6–9. It is also compared by scholars with older Mesopotamian flood traditions, including the Epic of Gilgamesh, though those accounts use different characters and details.