Currently you’re unable to fully integrate scales with the Square app to price items by weight. This is a popular feature request, so we’ll be sure to make an announcement if it becomes available.
In the meantime, the following options allow you to price items by weight:
Use a third-party scale and the Square app’s variable pricing feature to process these types of transactions.
E.g. Pre-program the weights of your items in the scale and enter those prices during the time of sale using a variable priced item.
Use individual items as a specific measure of weight.
E.g. Set a price of X for an item called 'Tenth of Pounds'. If an item is 3.2 pounds, enter a quantity of 32.