What is the required diameter for the waste outlet of bathtubs?

The required diameter for the waste outlet of bathtubs is typically specified as 1 1/2 inches. This size is mandated in order to ensure adequate drainage performance for the volume of water that bathtubs typically hold and to prevent blockages from occurring due to insufficient drainage capacity.

Bathtubs often discharge a large quantity of water quickly when emptied, and having a larger diameter for the waste outlet helps facilitate this swift drainage. A 1 1/4-inch outlet may not provide sufficient flow capacity, especially under specific conditions where multiple fixtures may drain simultaneously.

Having the correct diameter not only ensures compliance with plumbing codes but also supports the overall functionality and efficiency of the plumbing system, reducing the chances of potential backups and plumbing issues in the future.