By default, the Unit of Measure feature is on. If it's not, you can turn it on by clicking on Company Preferences (gear icon) and search for Units of Measure.

1- Go to Units of Measure

2- Add a new Unit of Measure (U/M) Set

3- Click on Others

4- Define the Base Unit (Smallest Unit)

(Note: this need to be usually the smallest Unit: in our example it can not be the box and needs to be Piece)
Type the name and the abbreviation you going to use, in printouts it will use the abbreviation to use less space.
Then Click Next

This is the most important part
Type the name of your Larger Unit example( Box, Carton, Pallet)  
Note: you can have multiple units example 100 Pieces per Box and 36 Box Per Pallet and 24 Pallets Per Container but we make it simple here so we just add Box

Important Note:
if you are going to reuse this U/M for many other products we highly suggest to Check Mark 1- Unit value varies based on item., So what this give you is instead of saying 100 Pieces per box you can define how many Pieces per box when you crating the actual product item.

This is the best way to use this feature so you don't have hundreds of worthless U/M in your system

Make sure you ADD NEW First (2-)
Then (3-) Next

6-Select Default Units of Measures 

On this is step you select what to automatically load when you Buy or Sell 

7-Final Step to create the UM set - Name the Unit of Measure 

Example (PC/Box)

8-Select the Unit of Measure for your Item

Now We go back to your Item the you like to assign the new UM

Type how many Piece is in each Box.

Now when yo buy or sell you can select how you like to buy.

Advance Example: of Square Feet, Carton, Pallet and SQ Meter

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