According to Genesis, Noah’s Ark rested on the mountains of Ararat after 150 days of prevailing floodwaters.
Genesis 7:24 says the waters prevailed upon the earth for 150 days, and Genesis 8:4 then says that the Ark came to rest on the mountains of Ararat in the seventh month, on the seventeenth day of the month. The narrative therefore connects the resting of the Ark with the end of that 150-day period.
This number is often confused with the forty days and nights of rain. Genesis gives forty days for the rainfall, but describes the waters as prevailing for 150 days. The account also includes later waiting periods while Noah tested whether the ground had dried.
The date system in Genesis uses months and days, but the text does not identify those months with a modern calendar. The clearest direct numerical answer is 150 days.