You should first enable the feature. Go to "Settings," then "Inventory." You will find an option for "Units of Measure" in products you have to Activate it. Next, go to the "Inventory app" and then "configuration" You will find the "Unit of Measure" option at the end of the menu "UoM categories".

Hi,
If you have enabled multi unit of measure feature in your database, you can find the unit of measure from sales or purchase or inventory application.

From sales application, you can see Unit of measure menu and in other apps, if you open Unit of measure categories, you can see the related unit of measures.

Thanks & Regards

Walnut Software Solutions