This drain trap is meant to replace the default plastic trap you may have that always gets displaced by the water, or that you don't have and large debris just goes down the drain.
The largest outer diameter of the bottom of the trap is about 49.5 millimeters, and is very gently tapered so it is narrower at the bottom-most point by about 1 millimeters.
The upper flange [what is visible at the surface when seated in the sink] has a diameter of about 71 millimeters. the smallest holes in the trap are about 3 millimeters wide.
The image in the pictures is from a stainless steel example.