labor costs also are ordinarily divided into direct and indirect categories. Direct labor
costs are those that can be conveniently and easily charged to the product or service in
question. Other labor costs, such as for supervisors, material handlers, and design engineers,
are charged as indirect labor and are thus included as part of overhead costs. It is often
imperative to know what is included in direct labor and direct material cost data before
attempting to use them in engineering economy studies.
In addition to indirect materials and indirect labor, there are numerous other cost items
that must be incurred in the production of products or the rendering of services. Property
taxes must be paid; accounting and personnel departments must be maintained; buildings
and equipment must be purchased and maintained; supervision must be provided. It is
essential that these necessary overhead costs be attached to each unit produced in proper
proportion to the benefits received. Proper allocation of these overhead costs is not easy,
and some factual, yet reasonably simple, method of allocation must be used.
As might be expected, where solutions attempt to meet conflicting requirements such
as exist in overhead-cost allocation, the resulting procedures are empirical approximations
that are accurate in some cases and less accurate in others.
There are many methods of allocating overhead costs among the products or services
produced. The most commonly used methods involve allocation in proportion to direct labor
cost, direct labor hours, direct materials cost, sum of direct labor and direct materials cost,
or machine hours. In these methods, it is necessary to estimate what the total overhead costs
will be if standard costs are being determined. Accordingly, total overhead costs are customarily
associated with a certain level of production, which is an important condition that should always
be remembered when dealing with unit-cost data. These costs can be correct only for the
conditions for which they were determined.
To illustrate one method of allocation of overhead costs, consider the method that
assumes that overhead is incurred in direct proportion to the cost of direct labor used.
With this method, the overhead rate (overhead per dollar of direct labor) and the overhead
cost per unit would respectively be