Electrical Estimating Methods, 4th Edition

CHAPTER 2 Types of Estimates

Estimators use four basic types of estimates. These types may be referred to by different names and may not be recognized by all as definitive. Most estimators, however, will agree that each type has its place in the construction estimating process. The four types of estimates are as follows:

• Order of magnitude estimate. The order of magnitude estimate could be loosely described as an educated guess. It can be completed quickly. Accuracy will vary between 20% and 25%.
• Square foot estimate. This type is most often useful when only the proposed size and use of a planned building is known. This method can be completed within an hour or two. Accuracy can be plus or minus 15%.
• Assemblies estimate. A systems estimate is best used as a budgetary tool in the planning stages of a project when some parameters have been decided. This type of estimate could require as much as one day to complete. Accuracy is expected to be plus or minus 10%.
• Unit price estimate. Working drawings and full specifications are required to complete a unit price estimate. It is the most accurate of the four types but is also the most time consuming. Used primarily for bidding purposes, the accuracy of a unit price estimate can be plus or minus 5%.

As an estimator and his or her company gain repetitive experience on similar or identical projects, the accuracy of all four types of estimates will improve dramatically. In fact, given enough experience and the historical data backup, ...