Lang factor

In industrial engineering, the Lang factor is a ratio of the total cost of installing a process in a plant to the cost of its major technical components.

The factors were introduced by H. J. Lang in "Chemical Engineering" magazine in 1947 as a method for estimating the total installation cost for plants and equipment.

These factors are widely used in the refining and petrochemical industries to help estimate the cost of new facilities. A typical multiplier for a new unit within a refinery would be in the range of 5.0. This means if you add up the purchase price of all the pumps, heat exchangers, pressure vessels, and other process equipment, then multiply that cost by 5.0, you will obtain a rough estimate of the total installed cost of the plant, including equipment, materials, construction, and engineering. The accuracy of this estimate method usually is +/- 30%.

The factors change over time because construction labor, bulk materials (concrete, pipe, etc.), engineering design, indirect costs, and major process equipment prices often do not change at the same rate.

In the late 1960s and early 1970s Kenneth Guthrie further expanded on this concept, generating different factors for different types of process equipment (pumps, exchangers, vessels, etc.), so these are sometimes referred to as "Guthrie factors".