In default product page we do not display inventory in each product in order that the access to the product page will be faster. But if you need to see the inventory on the product page, you can activate the settings below.
I. Activated this Feature in Setup Menu
Step 1. Select module on setup menu
Step 2. Tab product then set Inventory Always Rendered to "yes"
II. How to use this Function
in Product menu the system will display unit quantity automatically
Watch video how to setup show quantity in Menu Product