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.

PS4 Controller Touchpad

Joyonway PB554 Capacitive Touch spa touchpad - spatex - Australian Distributor, trade sales

JCD Joystick Controller Touchpad Board For PS4 Slim Pro 4.0 5.0 CUH-1000/1100 JDM-030 JDS-040 Gamepad Touch Pad W/ Flex Cable - AliExpress

Steam Deck - Wikipedia

Game Controller Repairing Touch Pad Accessory, Wearable and Durable Replacement Touchpad for PS4 Gamepad : Video Games

eXtremeRate Replacement D-pad R1 L1 R2 L2 Triggers Touchpad Action Home Share Options Buttons for ps4 Controller, Chrome Gold Full Set Buttons Repair Kit for ps4 Slim Pro CUH-ZCT2 Controller – eXtremeRate

Inaudible Discussion

Powkiddy X28 Handheld Game Player Android 11 T618 5.5 Inch Touch IPS Screen Handheld Retro Game Console Gift Free Shipping - AliExpress

PlayStation Controller Dimensions & Drawings