What is the minimum size of a P-trap drainpipe?

The minimum size of a P-trap drainpipe is typically 1.5 inches. This dimension is standard for most residential applications, especially for sinks, which helps ensure adequate drainage and prevents clogs. A 1.5-inch P-trap is designed to provide sufficient capacity for waste flow while maintaining the necessary water seal to prevent sewer gases from entering the living space.

While larger sizes like 2 inches or 3 inches may be utilized in specific applications, such as for larger fixtures or in commercial plumbing systems, the common residential standard remains at 1.5 inches for kitchen sinks and bathroom sinks. This size strikes a balance between effective drainage and practicality within typical plumbing systems.