Ars calculates the size of the DualShock 4 touchpad: about 2.1” x 1”

A little image wrangling (and math) generates a general sizing estimate.

The New Playstation 4 Controller W Touchpad LED PS4

PlayStation Controller Dimensions & Drawings

A data-driven approach to predicting consumer preferences for product customization - ScienceDirect

February, 2013

Smart controller: Introducing a dynamic interface adapted to the gameplay - ScienceDirect

PlayStation Controller Dimensions & Drawings

Ars Technica

Almohadilla térmica Hotties para roedores y conejos!, almohadilla térmica

PS4 Controller Touchpad