Types of Estimates:
There are several kinds of estimating techniques; these can be grouped into two main categories

1. Approximate estimates
2. 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.
(b). Total quantity method.

(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. labour, 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:
(I) Materials
(II) Labour
(III) Plant/Machinery
(IV) Sundries & Contingencies
(V) Overheads & Profit.

The total quantities of each kind or class of material or labour are found and multiplied by their individual unit cost. Similarly, the cost of plant, overhead expenses and profit are determined. The costs of all the five sub-heads are summed up to give the estimated cost of the item of work. For example, the cost of brickwork in a building would be determined as below:

I ( i ) Cost of Materials at the source Rs. xxxxx

Bricks Rs. xxxxx

Sand Rs. xxxxx

Cement Rs. xxxxx

Water & Electricity Rs. xxxxx

(ii) Cost of Handling and transporting above materials Rs. xxxxx
II Cost of Labour, both skilled and unskilled Rs. xxxxx
III Cost of plant/machinery Rs. xxxxx
IV Sundries & Contingencies Rs. xxxxx
V Overhead & Profit Rs. xxxxx

Total Cost of Brickwork Rs. xxxxx


Data Required for Preparing an Estimate
In order to prepare a detailed estimate the estimator must have with him the following data:

1. Plans, sections and other relevant details of the work.
2. Specifications indicating the exact nature and class of materials to be used.
3. The rates at which the different items of work are carried out.

To enable an estimator to take out the quantities accurately, the drawings must themselves be clear, true to the fact and scale, complete, and fully dimensioned. The estimator has also to bear in mind certain principles of taking out quantities.

Steps in Preparation of an Estimate:
There are three clearly defined steps in the preparation of an estimate.

1 . Taking out quantities
In the first step of taking out quantities, the measurements are taken off from the drawings and entered on measurement sheet or dimension paper. The measurements to be taken out would depend upon the unit of measurement. For example, in the case of stone masonry in superstructure, length, thickness and height of the walls above plinth level would be taken out from the drawings and entered on the measurement sheet, whereas, in the case of plastering only the lengths and heights of the walls would be entered. Obviously, the unit of measurement in the first case is cubic meter and that in the second case is square meter

2. Squaring out
The second step consists of working out volumes, areas, etc. and casting up their total in recognized units.

3. Abstracting
In the third step all the items along with the net results obtained in the second step are transferred from measurement sheets to specially ruled sheets having rate column ready for pricing. The second and third steps above are known as working up. All calculations in these stages and every entry transferred should be checked by another person to ensure that no mathematical or copying error occurs. An estimating/ documentation software will be handy while doing these type of work.

Qualifications of an Estimator

A good estimator should possess the following quantifications:
1. A thorough understanding of architectural drawings.
2. A sound knowledge of building materials, construction methods and customs prevailing in the trade.
3. A fund of information collected or gained through experience in construction work, relating to materials required with a clear understanding of its alternatives and substitutes, hourly output of workers and plant, overhead expenses and costs of all kinds.
4. An understanding of a good method of preparing an estimate.
5. A systematic and orderly mind.
6. Ability to do careful and accurate calculations.
7.Ability to collect, classify and evaluate data that would be useful in estimating.

Thus an estimator should always be alert in preparing estimates as he has to choose from a vast ocean of data. Collecting, classifying, evaluating and presenting it in a systematic way is not a simple task. Effective use of a tool, such as a software, can bring him a lot of ease and accuracy in his endeavor.

Labels: bill of quantity software, Construction estimating Software, estimator, preparing estimates, rate analysis

# posted by Anilkumar : 12:41 PM