# Rough Order of Magnitude

Continuing our last post about Order of Magnitude Estimate, today this article is about **Rough Order of Magnitude Estimate**. This is an example of Rough Order of Magnitude estimate. Order of Magnitude Estimate is one of several types of estimation methods which is used commonly in construction estimation. The method is by far the most uncertain estimate level used. As the name implies, the objective is to establish the order of magnitude of the cost, or more precisely, the cost within a range of +30 to –50%. Various techniques can be employed to develop an order-of-magnitude estimate for a project or portion of a project.

#### Rough Order of Magnitude

James E. Rowings, Jr. explained that when the object of the estimate is a single criterion, such as a piece of equipment, the order-of-magnitude cost can be estimated quickly based on the weight of the object. For the cost determination, equipment can be grouped into three broad categories:

- Precision/computerized/electronic
- Mechanical/electrical
- Functional

Precision equipment includes electronic or optical equipment such as computers and surveying instruments. Mechanical/electrical equipment includes pumps and motors. Functional equipment might include heavy construction equipment, automobiles, and large power tools. Precision equipment tends to cost ten times more per pound than mechanical/electrical equipment, which in turn costs ten times per pound more than functional equipment. Obviously, if you know the average cost per pound for a particular class of equipment (e.g., pumps), this information is more useful than a broad category estimate. In any case, the estimator should have a feel for the approximate cost per pound for the three categories so that quick checks can be made and order-of-magnitude estimates performed with minimal information available. Similar approaches using the capacity of equipment, such as flow rate, can be used for order-of-magnitude estimates.

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