The base template of a barcode label contains:
The base template page size is 1x1in (2.54x2.54cm)
What to consider when customizing barcode labels?
Define the barcode type to use - for example, you may want to print the Supplier item code while receiving items from your suppliers and the Registered barcode while selling items to your customers
Define the barcode standard - for example using barcode standard Code 128 is universal when keeping items in stock and tracking them, but while selling items you can have different barcode standards registered with the Global standard organization GS1
Define the barcode label size - depending on your printer or the label size of the sticker roll you may need to resize the PDF page accordingly.
Read more about customizing PDF templates.
Note: If you are doing stocktake with a barcode scanner you may want to have a batch barcode on your barcode labels. By customizing the template you can add multiple barcodes or replace item barcodes with batch barcodes.