In the Genesis Noah's Ark account, the floodwaters rose 15 cubits above the mountains.
Genesis 7:20 states that the waters rose fifteen cubits upward and covered the mountains. The statement occurs after the account says that the waters increased and the ark floated on the surface, emphasizing the overwhelming scale of the Flood within the narrative.
This number is separate from the ark's height, which Genesis gives as 30 cubits, and from its length of 300 cubits. Readers sometimes connect the fifteen-cubit figure to the vessel's dimensions, but the verse presents it as the depth by which the waters covered the mountains.
The passage is a theological narrative rather than a modern topographic survey. It does not identify which mountains are meant, provide a sea-level reference, or explain how the height was measured. The number is therefore a specific biblical detail, not a modern scientific measurement of global water levels.