To set up your units of measure you will need follow these steps:
Consider whether you will need to use additional trade units, i.e. if the stock item will be bought and/or sold using a different unit of measure to the stock unit.
If you need additional trade units, decide if you need to create units of measure specifically for your base units, or whether you can use the measures already identified.
Create your units of measure list.
Set the units of measure that are used in your product groups, using the product group Units of Measure tab. This enables those units to be used with associated stock items.
As a minimum, assign the stock unit. If you are using trade units, assign the base unit and select the selling and buying settings required for the measures.
Set the units of measure to use for your stock items. A stock item will use the units enabled in its product group.
What do you want to do?
Validate units of measure precision
Overview
Reference