What size trap does a bathtub use?

A bathtub typically uses a 1 1/2-inch trap due to its adequate capacity for handling wastewater while accommodating the flow rate of water draining from the tub. This size ensures that the trap can effectively prevent sewer gases from entering the home while also allowing for efficient drainage. The 1 1/2-inch dimension strikes a balance between sufficient volume to handle the drainage from the bathtub and maintaining a trap size that fits standard plumbing configurations. In contrast, larger trap sizes would be unnecessary and could complicate the plumbing system without providing any added benefit for bathtub drainage.