What is the minimum size for a bathtub drain outlet?

The minimum size for a bathtub drain outlet is correctly identified as 1 1/2 inches. This size is stipulated by plumbing codes to ensure adequate drainage and to prevent slower draining issues that could result from smaller pipes. A 1 1/2-inch outlet provides sufficient flow capacity to handle the outflow from a fully used bathtub, which is essential for both functionality and to minimize the risk of clogs.

Larger sizes, such as 2 inches, may be used in more complex or heavily used drainage systems, but they exceed the minimum requirement for a standard bathtub drain. On the other hand, both 1 inch and 1 1/4 inches are not suitable as they do not meet the established plumbing codes for minimum drainage sizes for bathtubs, leading to potential drainage issues.