Bathtubs. While there are no code requirements for tub size, minimum clear floor space alongside a bathtub should be at least 60 inches long (the length of a standard tub) and 30 inches wide. Always allow clear space for access to plumbing and/or whirlpool motors. Enclosed Showers If we recommend a minimum usable interior wall-to-wall dimension of 34 inches, 32 inches is allowable. The cabine shower enclosure require that all showers, regardless of shape, have a minimum finished interior of 1,024 square inches, with an interior circular diameter of at least 30 inches.