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. 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.
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.
Standard Method of Measurement of Building Works
The different methods of measuring used by various Central and State Government departments and by construction agencies were found to be a serious difficulty to estimators and a standing cause of disputes. For this reason a unification of the various systems at the technical level had been accepted as very desirable and wanting. Although the standard has no legal sanction and as such need not be adopted unless it is referred to in the contracts.
Principles of Deciding Unit of Measurement
A beginner may find it difficult to remember the units of measurement of different items. Memorizing of units of measurement would be greatly simplified if he knows the principles kept in view while selecting the units of measurements. Following are the most important principles of selection of unit of measurement:
1. The unit of measurement should be simple and convenient to measure, record and understand.
2. It should be one, which provides for fair payment for the work involved.
3. In the result it should yield quantities, which are neither too minute nor too large.
4. The price per unit should not be a very small figure or a very large one, that is, generally costlier items will be measured in smaller units, cheaper ones in larger units.
5. The unit of measurement may sometimes depend upon the unit for the raw material and/or labor and/or important dimensions.