Is there a size for the caliber of the drain of the flush toilet?

There are uniform standards.

There are three sizes of flush toilet outlet (floor drain),

There are three sizes of flush toilet outlet (floor drain):

The distance to the center of the floor drain from the wall as the base point,

are A:300mm;

B:400mm;

AB:350mm.

Expansion of the standard size of the toilet outlet (floor drain):

There is a standard size of the toilet outlet (floor drain).

Expanded Information:

Toilet seat drain size is generally about 80mm, the pipeline needs to be a diameter of 110 sewage pipe. Hole distance refers to the toilet drain center point to the wall size, each different toilet hole distance is not the same, therefore, in the purchase of toilet should pay attention to the measurement of their own home before the drain hole distance. Under special circumstances, you can use a distance changer, you can adjust the hole distance of about 50mm, but generally do not recommend the use of, may affect the smoothness of the drainage.

Reference:

Baidu Encyclopedia - Sewage Discharge Outlet