Order of Magnitude Estimate
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.
Wikipedia explains that an order of magnitude estimate is prepared when little or no design information is available for the project. It is called order of magnitude estimate because that may be all that can be determined at an early stage. In other words, perhaps we can only determine that it is of a 10,000,000 magnitude as opposed to a 1,000,000 magnitude. Various techniques are employed for these estimates, including experience and judgment, historical values and charts, rules of thumb, and simple mathematical calculations.
Factor estimating is one of the more popular methods. This involves taking the known cost of a similar facility and factoring the cost for size, place, and time. Cost modeling is another common technique. In cost modeling the estimator models the various parameters of the facility and applies costs to the derived scope.
Building estimators or architects may use the Uniformat system of breaking down the building into functional systems or assemblies during the schematic design (SD) phase of planning and design. The RSMeans Square Foot Costs book organizes building costs according to the 7 divisions of the UNIFORMAT II classification system. They are :
- Equipment & Furnishings
- Special Construction
- Building Site Work
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