According to Genesis, how many cubits of water covered the mountains during the Flood?

Genesis says the Flood waters rose fifteen cubits above the mountains.

Genesis 7:20 states that the waters prevailed fifteen cubits upward, covering the mountains. This is separate from the Ark’s height, which Genesis 6:15 gives as thirty cubits. The two numbers are sometimes confused because both occur in the same narrative and use the same ancient unit.

The text does not explain whether the fifteen-cubit figure measures water above the highest mountain, a clearance needed for the Ark, or a literary measurement within the narrative. It simply presents the waters as high enough to cover the mountains. Since the historical length of a cubit is uncertain, converting fifteen cubits into metres is approximate. The number itself is the specific figure supplied by Genesis.