Cross reference
Genesis 7:17
17 The flood was forty days on the earth. The waters increased, and lifted up the ark, and it was lifted up above the earth.
Genesis 7:4
4 In seven days, I will cause it to rain on the earth for forty days and forty nights. Every living thing that I have made, I will destroy from the surface of the ground."
Genesis 7:12
12 The rain was on the earth forty days and forty nights.