There are several kinds of estimating techniques; these can be grouped into two main categories: Approximate Estimates and Detailed Estimates
1. Approximate Estimates
An approximate estimate is an approximate or rough estimate prepared to obtain an approximate cost in a short time. For certain purposes the use of such methods is justified.
2. Detailed Estimate
A detailed estimate of the cost of a project is prepared by determining the quantities and costs of every thing that a contractor is required to provide and do for the satisfactory completion of the work. It is the best and most reliable form of estimate. A detailed estimate may be prepared in the following two ways
(a) Unit Quantity Method
In the unit quantity method, the work is divided into as many operations or items as are required. A unit of measurement is decided. The total quantity of work under each item is taken out in the proper unit of measurement. The total cost per unit quantity of each item is analyzed and worked out. Then the total cost for the item is found by multiplying the cost per unit quantity by the number of units. For example, while estimating the cost of a building work, the quantity of brickwork in the building would be measured in cubic meters. The total cost (which includes cost of materials. labor, plant, overheads and profit) per cubic meter of brickwork would be found and then this unit cost multiplied by the number of cubic meters of brickwork in the building would give the estimated cost of brickwork. This method has the advantage that the unit costs on various jobs can be readily compared and that the total estimate can easily be corrected for variations in quantities.
(b) Total Quantity Method
In the total quantity method, an item of work is divided into the following five subdivisions:
The total quantities of each kind or class of material or labor are found and multiplied by their individual unit cost. Similarly, the cost of plant, overhead expenses and profit are determined.