Measure before you start PE!
Shortcut: Grab your penis behind the glans, and pull straight out to simulate your erect length. It won't be exactly the same, but you can track progress without having an erection.
Normal (grown man): 5 - 7 inches (12.7 - 17.8 cm).
Average (grown man): 5.5 - 6 inches (14 -15.25 cm).
Measurements vary from minute to minute! Compare with a toilet paper tube or other fixed=size item to watch your progress.
Normal length (grown man): 3 - 4.5 inches (7.6 - 11.4 cm).
Normal width (grown man): 1 - 1.5 inches (2.5 - 3.8 cm).