Process costing is used when there is mass production of similar products, where the costs associated with individual units of output cannot be differentiated from each other. In other words, the cost of each product produced is assumed to be the same as the cost of every other product. Under this concept, costs are accumulated over a fixed period of time, summarized, and then allocated to all of the units produced during that period of time on a consistent basis. When products are instead being manufactured on an individual basis, job costing is used to accumulate costs and assign the costs to products. When a production process contains some mass manufacturing and some customized elements, then a hybrid costing system is used.
Examples of the industries where this type of production occurs include oil refining, food production, and chemical processing. For example, how would you determine the precise cost required to create one gallon of aviation fuel, when thousands of gallons of the same fuel are gushing out of a refinery every hour? The cost accounting methodology used for this scenario is process costing.
Process costing is the only reasonable approach to determining product costs in many industries. It uses most of the same journal entries found in a job costing environment, so there is no need to restructure the chart of accounts to any significant degree. This makes it easy to switch over to a job costing system from a process costing one if the need arises, or to adopt a hybrid approach that uses portions of both systems.
Example of Process Cost Accounting
As a process costing example, ABC International produces purple widgets, which require processing through multiple production departments. The first department in the process is the casting department, where the widgets are initially created. During the month of March, the casting department incurs $50,000 of direct material costs and $120,000 of conversion costs (comprised of direct labor and factory overhead). The department processes 10,000 widgets during March, so this means that the per unit cost of the widgets passing through the casting department during that time period is $5.00 for direct materials and $12.00 for conversion costs. The widgets then move to the trimming department for further work, and these per-unit costs will be carried along with the widgets into that department, where additional costs will be added.
Types of Process Costing
There are three types of process costing, which are:
Weighted average costs. This version assumes that all costs, whether from a preceding period or the current one, are lumped together and assigned to produced units. It is the simplest version to calculate.
Standard costs. This version is based on standard costs. Its calculation is similar to weighted average costing, but standard costs are assigned to production units, rather than actual costs; after total costs are accumulated based on standard costs, these totals are compared to actual accumulated costs, and the difference is charged to a variance account.
First-in first-out costing (FIFO). FIFO is a more complex calculation that creates layers of costs, one for any units of production that were started in the previous production period but not completed, and another layer for any production that is started in the current period.
There is no last in, first out (LIFO) costing method used in process costing, since the underlying assumption of process costing is that the first unit produced is, in fact, the first unit used, which is the FIFO concept.
Why have three different cost calculation methods for process costing, and why use one version instead of another? The different calculations are required for different cost accounting needs. The weighted average method is used in situations where there is no standard costing system, or where the fluctuations in costs from period to period are so slight that the management team has no need for the slight improvement in costing accuracy that can be obtained with the FIFO costing method. Alternatively, process costing that is based on standard costs is required for costing systems that use standard costs. It is also useful in situations where companies manufacture such a broad mix of products that they have difficulty accurately assigning actual costs to each type of product; under the other process costing methodologies, which both use actual costs, there is a strong chance that costs for different products will become mixed together.
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