The discussion has described methods by which all factory overhead costs, for both producing and service departments, are assigned to work in process by using factory overhead rate in the producing departments only. However, it is possible to assign certain service department costs directly from the service department to work in process. For example, materials handling costs can be accumulated in a materials handling department, and an overhead rate based on materials can be used for assigning those costs directly to work in process. An overhead rate based on materials is calculated by dividing the materials handling costs by a selected measure of materials usage, such as materials cost, material weight, or the number of materials items or pieces used.