31 Heb “rose fifteen cubits.” Since a cubit is considered by most authorities to be about eighteen inches, this would make the depth 22.5 feet. This figure might give the modern reader a false impression of exactness, however, so in the translation the phrase “fifteen cubits” has been rendered “more than twenty feet.”
32 Heb “the waters prevailed fifteen cubits upward and they covered the mountains.” Obviously, a flood of twenty feet did not cover the mountains; the statement must mean the flood rose about twenty feet above the highest mountain.

In other versions

The waters prevailed above the mountains, covering them fifteen cubits deep.

The waters rose and covered the mountains to a depth of more than fifteen cubits.

The mountains were covered as the water surged above them more than twenty feet.

rising more than twenty-two feet above the highest peaks.

The waters swelled fifteen cubits above the mountains, covering them.

Fifteen cubits upward did the waters prevail; and the mountains were covered.

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