The amount of water or other substance that a bathtub can hold; the capacity of a single bathtub.
English bathtub + -ful suffix. This is a standard unit measurement following the pattern of spoonful, cupful, etc.
A typical bathtubful contains about 80-100 gallons of water—that's more water than many people use in a day for all activities combined, which is why baths are considered less water-efficient than showers!
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