What is the standard size of a residential toilet supply line?

The standard size of a residential toilet supply line is 1/2 inch. This size is commonly used because it provides sufficient water flow for the toilet's flushing mechanism while being small enough to fit in standard plumbing fixtures. A 1/2 inch supply line can efficiently handle the necessary water pressure and volume without taking up excessive space or requiring larger fittings, which could complicate installation and increase costs.

Other sizes, such as 3/4 inch or 1 inch, are typically used for main water supply lines or larger fixtures requiring more water flow, while 5/8 inch is not a standard size for toilet supply lines and is less commonly encountered in residential plumbing. Thus, 1/2 inch is recognized as the industry standard for this application.