What is an Estimation and types of estimates?
Estimation is a rough assessment or computation used to determine the worth of the proposed work or activity period. The estimate will be beneficial in determining the amount of time required to complete a task or activity, as well as the resources required, such as labor and budget.
The estimated value may be closer to the actual cost to be incurred, but it is not always the same. The cost estimate is based on resources such as manpower, machinery, material quality standards, and building process.
The precision of the planning is determined by the accuracy of the estimations. However, the estimates must be made in such a way that the actual cost will be within 10% of the projected amount (assuming the contractor profit of 10% of project cost).
For Example: Construction of Roads, Buildings, Railways, Canals, etc.
The estimated cost is calculated by comparing similar projects. The approximate cost may be calculated using techniques that are based on a building’s area or cubic content, and then multiplied by an estimated rate for the unit of area or cubic content.
For a proposed drawing, approximate amounts of materials and labor required per Sqm. or Cum. can also be obtained.
TYPES OF ESTIMATES
1. Detailed Estimate
Task-specific dimensions, such as length, width, and depth/height, as well as quantities, are included in detailed estimates. This estimate is prepared in detail prior to inviting of tenders, i.e. after receiving administrative approval.
Unit – measures the unit of work in Cum./Sqm./Nos/Rm
L – Length
B – Breadth or Width
D – Depth or thickness
The entire project is divided into sub-works, and the quantities of each sub-work are calculated separately. The dimensions of the required work are taken from the drawings of the project.
2. Abstract Estimate
An abstract estimate is created based on the detailed estimate. This includes quantities, rates, and amounts specific to each work.
In this estimate, Length, Width and Depth are not specified. Direct quantities are taken over here from detailed abstract. Rates are to be taken from applicable schedule of rates documents.
3. Detailed cum Abstract Estimate
This is a combination of detailed and abstract estimates. It gives task wise dimensions i.e. Length, Width, Depth, Quantity, Rate and Amount. This sort of estimate is often created for small and simple projects.
BASIC COMPONENTS OF THE ESTIMATE
There are several components of estimates that must be worked out in order to arrive at a final estimate. They’re listed below.
1. Description of work/task/activity
To begin any task, one must acquire information such as the name of the work, the purpose of the work, the location of the work, and the work’s salient features, among other things.
2. Dimensions of the work/task/activity
Each work shall have the basic details like length, width, depth/thickness, plan and cross sections, elevations showing the length, width, thickness/depth and other important parameters.
3. Designs and Drawings
The designs will be prepared based on the soil conditions, loads, functional requirements, and other parameters. Based on these parameters, the length, width and other dimensions are decided.
Drawings are to be prepared to the scale for the purpose of the visual representation of structure. It gives more clarity about the structure. Design will consists of cross sectional dimensions, drawings, reinforcement details and so on.
4. Specification of work
A specification report is a document that lists all of the requirements included in the estimate in brief detail. The work requirements should be able to be determined by reading the specification report.
The construction material and technique of various components of the structure are also specified in the specifications.
5. Detailed quantities of the task
To arrive the estimated amount of work we need to have the detailed quantities of all the tasks which are to be executed. The quantities of tasks shall be arrived at by multiplication of the measurement of length, width and depth depending on the type of task.
The quantities may be in cubic meter, Square meter, meter or in number. We should know about the unit of measurement of each task. The units may be in cubic meter, Square meter, meter or in number also.
- Earthwork, Concrete work measured in Cubic meter
- Plastering, Painting, Flooring measured in Square meter
- Cement, Steel measured in metric tonne
- Bricks measured in numbers
- pipe length measured in running meters
Rates are essential to calculate the estimated amount of work. the rates shall be adopted from the approved and applicable schedule of rates. Schedule of rates (SoR) is a document in which the details of rates of unskilled labor, semiskilled labor, skilled labor, material rates and conveyance rates, which are to be adopted, are published every year.
These rates may be directly adopted or shall be used for deriving rates of the tasks. Each department of government may have different schedule of rates in some states and similar schedule of rates in other states.
The schedule of rates is prepared by a committee of chief engineers based on the market rates appointed by the government. The rates in SoR will change every year as recommended by the Board of Chief Engineers based on the prevailing market rates.
- Skilled Labor (Manpower) – Rs. 500 per person per day
- Cement Bag (Material)- Rs. 250 per bag
- Excavator (Machinery) – Rs. 2000 per hour
7. Lead Statement
A lead statement is a document that is used to calculate the cost of conveying materials from the source to the work site. The lead statement contains details of the materials required, the initial rate of material, units, and distance in kilometres from the source to the work site, as well as conveyance and blasting charges, among other things.
The rate of each material shall be calculated using the rates approved in the SoR’s. Furthermore, seigniorage charges for the material must be calculated using the government’s approved rates and added to the estimate.
It is the horizontal distance from source to work site to transport the material.
It the horizontal distance to carry the material on the head from source to work site.
For example, the cost aggregate stone varies from distance of quarry to work site. The cost of one load of aggregate stone brought from a quarry away from 20 km distance will be more when compared to the stone brought from a quarry away from 5 km distance.
Additional Head Lead
The part distance or up to 10m horizontal distance over and above the initial lead of 10m is called as additional head lead. For example, In a total head lead of 25m, one initial lead and two additional head leads are involved.
This is to say, in a road network, the labor carrying head load of soil from 30 meters carried on head from pit to road embankment should get more rate when compared to the labor carrying head load from 10 meter distance.
It is the vertical height/distance from the source to the work spot to carry and place the material. For Example, If the vertical distance from earthwork pit to the tap of the earthen embankment of an irrigation tank is 10m. The lift here is 10m.
It is the vertical height/distance from the source to the work spot to carry and place the material on the head. In the above example, if the laborers are carrying earth on their head, 10m is called head lift.
Additional Head Lift
The part distance or up to 2m vertical distance over and above the initial lift of 2m is called as additional head lift. For example, In a total head lift of 5m, one initial lift and two additional head lifts are involved.
8. Report accompanying the estimate
In conclusion, in order to prepare an estimate, we need rates for all materials, machines, labor, drawings specifications, data processing, and detailed measurements, among other things.
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