Net weight is defined as the total weight of an item (gross weight) minus the weight of any containers or packaging also contained within the gross weight. To determine the net weight you must know both the total weight of the object and the tare weight -- or the weight of everything except the item you are seeking the net weight for. Net weights are often used in scientific experiments or food distribution to ensure the weight referenced does not include extraneous items. Determine the gross weight of the object of interest by placing the object, including the container or packing, on the scale. Write down the reading on the scale, known as the gross weight. Remove the object of interest from the container or packaging and place aside. Place all of the packaging or the containers on the scale and record the total weight, known as the tare weight. Subtract the tare weight from the gross weight using a calculator to obtain the net weight.