What is the estimation process?

The estimation process is the process of calculating the estimation of the total work to be done. For all engineering projects, it is much necessary to know the probable cost of construction before the work is undertaken. This probable cost is known as the cost estimate or estimation of the project. The estimation process has a good scope in project management as no project can start before the proper cost estimate and project budget. The estimation of the project includes the cost of materials, plants, transportation, scaffoldings, labors, hours of labor, tools, taxes, supervision, and profit of the contractor.

Importance of estimation in project management

Estimation plays a very important role in project management as all the components of projects are dependent on it. Hence, it is much needed that the project manager should prepare the cost estimate properly. If the cost estimate is more than the money available, then the project cost exceeds, and various attempts are made by the project manager to reduce the project cost, such as varying the proportions, changing specifications, reducing the work, reducing the person-hours, and so on. If the cost estimate is less than the money available, then the project is considered extra profitable and additional expenses can be done as per the client’s requirements.

The main problem during estimation that the project managers mostly face is the exceeding of cost estimate. This happens due to exclusion of some items, changing the design at the last moment, improper rates of materials, inaccuracy in estimation, involvement of the third party for distribution or arrangement of materials, and so on. Even small inaccuracies lead to an excessive rise in final project costs. Hence, it is much important to prepare the estimate precisely.

Recommendations for preparing a proper estimate

For preparing a correct estimate, the following points should be taken into consideration:

• Preparation of an effective work breakdown structure is necessary for preparing a good estimate.
• Dimensions of all the items should be measured properly.
• No item should be excluded.
• The rates of the items should be reasonable.

Project estimation techniques

There are two major types of estimation techniques of a civil engineering project:

• Approximate Estimate
• Detailed Estimate

Approximate estimate

An approximate estimate is also known as a rough estimate. This estimation technique is used to get the probable cost of the project in a very short time. This method does not contain any detailed measurements and calculations. Assumptions are made for most things. Hence, it is not usually used during project management of important structures. This estimation just gives a rough idea about the probable cost estimate. Given below are the various methods of approximate estimation for buildings:

• Plinth area method
• Cubic contents method
• Service unit method
• Bay method
• Cost comparison method
• Cost from materials method

Detailed estimate

The detailed estimation technique has a wide scope in all projects. In this estimation technique, the estimation is carried out in two steps. Initially, the quantities of different items are calculated and then the cost is worked out.

Calculation of items

For the proper project management, first, the whole work is distributed into various parts of works, such as earthwork, brickwork, concrete work, and so on. Then the items are divided into various subgroups and the quantities of each item are computed.

Estimated cost calculation

In estimating process, the per-unit cost of each item is taken into consideration as per the standard rates of the market and the total cost is worked out by multiplying the total number of items by the cost. An additional 3% to 5% of the total cost estimate is added for the future contingencies. Also, an additional cost of 1.5% to 2% of the total cost estimate is added to the total project budget estimation for the expenses of the work-charged establishment.

There are some other types of estimation techniques of a project in other domains except civil engineering:

• Top-down estimation
• Software cost estimation
• Use case point estimation
• High-level estimation
• Three-point estimation

Top-down estimate

The top-down estimate technique is used only in the initial stages of a project when the complete data about the project is not available. In this method, project managers and other experienced staff discuss thoroughly and find the total estimate of the project from the experience of past projects.

Software cost estimation

Software cost estimation is the calculation of total efforts required for the development of any software. Various models are being developed for estimating process. One of such models is COCOMO II. COCOMO II (Constructive Cost Model II) is a model used for software cost estimation, developed by Barry Boehm.

Use case point estimation

Use case point estimation technique is a software estimation process that is used to predict the size of a particular software project. Function point analysis is an important method used to size the software. The function point analysis works based on the user’s requesting and receiving functionality.

High-level estimation

In high-level estimation, various possibilities of completing a project are determined and a maximum possible estimate is calculated approximately.

Three-point estimation

In a three-point estimation, three probable types of estimates are prepared, namely best-case estimate, most likely estimate, and worst-case estimate by predicting the best possible situation, most likely situation, and worst possible situation respectively.

Main items considered in the estimation

Earthwork

The quantity of earthwork is calculated in cubic meters. Earthwork in excavation and earthwork in the filling is calculated separately. The volume of earthwork in excavation is calculated as length x breadth x height of the excavation. The volume of earthwork in plinth fillings is calculated as length x breadth of the internal dimensions of the plinth.

Concrete in foundation

The quantity of concrete is calculated in cubic meters. The volume of concrete is taken as length x breadth x thickness. The length and breadth are the same as that of the excavation, the thickness varies as per the requirement. The thickness of concrete ranges between 20 cm to 45 cm, usually 30 cm is considered.

RCC work

RCC work in structure is calculated in cubic meters. The quantity of RCC work is calculated as length x breadth x height and the dimensions are calculated properly from the project plans. The quantities of RCC include centering, shuttering, and binding of reinforcement, but it does not include the quantity of steel reinforcement and its bending. The quantity of steel required is calculated separately in quintals. The quantity of reinforcement steel required is considered as 0.6% to 1%, usually assumption of 1% of the total RCC work is made.

Flooring and roofing

For the ground floor, usually finishing of tiles or cement concrete is done. The quantity is calculated in square meters. For the structure above ground level, that is the upper floors, the supporting structure is calculated in cubic meters and the floor finish is calculated in square meters. For roofs, the supporting structure is calculated in square meters and the lime terrace concreting is calculated in square meters.

Plastering

The plaster is usually considered 12 mm thick. It is calculated in square meters. For plastering of walls, the quantity is calculated for both faces of the walls separately.

Doors and windows

The quantity of door and window frames is calculated in cubic meters. The length, width, and thickness of each frame are calculated and multiplied to get the total volume.

Context and Applications

The estimating process has a scope for the students who are undertaking the following courses:

• Bachelors of Technology (Civil Engineering)
• Masters in Technology (Quantity Surveying)
• Masters in Technology (Construction Management)

Practice Problems

1. What is an approximate estimate known as?

1. Detailed Estimate
2. Rough Estimate
3. Unit weight Estimate
4. Plinth Area Estimate

Answer- b

Explanation: Approximate estimate is also known as a rough estimate.

2. What is the range of additional cost percentage considered for future contingencies?

1. 3% to 5%
2. 10% to 12%
3. 1.5% to 2%
4. 4% to 7%

Answer- a

Explanation: The range of additional cost percentage considered for future contingencies is 3% to 5%.

3. What is the range of quantity of steel reinforcement required for RCC work as that of the total RCC work?

1. 0% to 1%
2. 0.6% to 1%
3. 1.5% to 2%
4. 0.5% to 0.8%

Answer- b

Explanation: The quantity of steel reinforcement required for RCC work is considered 0.6% to 1% of the total RCC work.

4. What is the unit of measurement of plastering?

1. Meters
2. Square meters
3. Cubic meters
4. None of the above

Answer- b

Explanation: The unit of measurement of plastering is square meters.

5. What is the range of thickness of concrete in the foundation?

1. 10 cm to 20 cm
2. 30 cm to 45 cm
3. 50 cm to 60 cm
4. 20 cm to 45 cm

Answer- d

Explanation: The thickness of concrete in the foundation ranges between 20 cm to 45 cm.