In construction projects, precise estimation is crucial for successful execution. It facilitates procuring the right materials, managing resources efficiently, and preventing delays or cost overruns. Various methods are adopted for quantity estimation in the construction industries, each with advantages and limitations. These methods range from traditional manual estimation to software tools and advanced building modeling technologies such as Building Information Modeling (BIM).
In quantity estimation, two key factors must be carefully considered; completeness and accuracy. It is essential to ensure that every single item depicted in project drawings and specifications is considered during the estimation process. On the other hand, accuracy in quantity estimation is equally important. Accuracy refers to the precision and reliability of the estimated quantities and measurements; which means the estimated quantities align closely with the actual requirements of the project, minimizing discrepancies and deviations between the estimated and actual usage of materials and resources.
In this article, we will focus on manual quantity estimation, because in Pakistan’s construction industry, manual estimation is generally used, however, it consumes more time and has more chances of human errors. To minimize the calculation time and reduce the chances of errors Excel sheets are used for calculation. Another reason for using Excel is that data can be easily updated in response to design changes or other project modifications.
Quantity estimation can start after the finalization of the structural design. We will discuss here the quantity estimation of reinforced concrete footing. A step-by-step approach to estimation is listed below:
Gathering Essential Data
Quantity estimation kicks off with the collection of essential data. These include the footing layout plan with details such as the number of footings and the dimensions of each footing and footing section, including thickness, depth from Natural Ground Level (NGL) and reinforcement detail. Additionally, material specification like concrete strength and filling material is also required.
Preparation of Items List
With the data in hand, the next step involves carefully compiling the items list, which is depicted in the drawings. Main items include excavation, formwork, backfill, concrete, lean concrete, and reinforcement. Additionally, imported fill, bitumen coating, stone soling, isolation joint, expansion joint, and water stoppers can be added to the items list if mentioned in the provided drawings and specification
Preparation of Excel Sheet and Estimation
Prepare a calculation sheet in Excel, which simplifies the calculation process and reduces the chances of human error, however, the sheet will be prepared carefully, and after preparation sheet will be verified with the manual calculation.
In the verified sheet, we will input all required data carefully and get the estimation quantity.
Example of Quantity Estimation through Excel
For an example of estimation through Excel sheet, I have attached an Excel sheet of “Quantity estimation of reinforced concrete footing” in the below link.
Please use it and provide any comments or suggestions for further improvement.
Limitation of Attached Excel sheet
- It included only the following items:
- Excavation
- Concrete
- Lean concrete
- Stone Soling
- Reinforcement
- Backfill/Imported fill
- This sheet is applicable to eight types of footing.
- This sheet can be used for all types of footing, however, for footing size greater than 3m; all lap length reinforcement quantity will be manually calculated and will be added with the reinforcement quantity calculated from the sheet.
Conclusion
- Two Key factors of quantity estimation are the following:
- No items have been missed in quantity estimation list
- Accurately estimation is done
- Excel sheet is used in the estimation process due to the following:
- It provides accuracy in the calculation and saves the calculation time.
- It is easy to use, so, everyone can develop a sheet according to their requirement.
- Data can be easily updated, if there is any change in the design.
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