What does the term “fixture unit” measure in plumbing?

The term “fixture unit” is a measurement used in plumbing to estimate the probable demand for water that a fixture will require. It provides a standardized way to quantify the workload placed on a plumbing system by various fixtures, such as toilets, sinks, and bathtubs. Each type of fixture is assigned a specific value, known as a fixture unit, which represents its expected water consumption and usage patterns over time.

Understanding fixture units is critical for plumbing design, as it helps engineers and contractors determine the appropriate sizing of pipes, drains, and water supply systems to ensure they can adequately supply the necessary water pressure and flow for all fixtures without overloading the system. This measurement allows for efficient and effective planning of plumbing layouts in residential and commercial buildings.

The other options don’t capture the essence of what fixture units represent in plumbing. The physical size of a fixture pertains to its dimensions, the total cost relates to budgeting and purchasing rather than hydraulic design, and installation time is concerned with labor rather than water demand.