A conventional bathtub contains around 35 to 50 gallons of water and measures 60 inches length by 30 inches wide. Larger tubs, including soaking tubs or freestanding tubs, can contain up to 80 gallons of water. The average spa or corner tub holds 70 to 120 gallons of water.
A 10-minute shower, on the other hand, can use up to 50 gallons of water, depending on the type of showerhead used. To get the maximum volume of a bathtub, multiply the inner width, length, and depth in inches, then divide the result by 1,728 to convert it to cubic feet. The volume of the tub is then calculated in gallons by multiplying the total number of cubic feet by 7.5, the number of gallons in one cubic foot.
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