Revit includes geometric attribute parameters such as length, width, height, area, and volume for model components. These parameters form the foundation for BIM-based quantity calculation and cost estimation. Currently, there are three primary methods used for calculating engineering quantities and budgeting costs based on BIM.
(1) Extracting Data from BIM Design Software via API
Extracting quantity information through APIs directly from BIM design software and importing it into cost budgeting software allows for precise quantity retrieval of modeled entities. Additionally, it enables calculation of quantities for non-entity models that are difficult or impossible to model within BIM software by leveraging the geometric attributes of related entity models.
For example, quantities for reinforced concrete beams can be obtained directly from the model. However, beam templates not modeled cannot be extracted directly. By programming relevant calculation rules into a plugin, the quantities of these beam templates can be accurately computed using the geometric parameters of the associated beams. This improves both the accuracy and completeness of quantity calculations and cost budgeting.
This approach reduces the need for a fully complete and accurate BIM model. Since the base data for quantity calculation comes from geometric parameters extracted from the BIM model, real-time updates of quantities and costs can be synchronized with the BIM model. This facilitates dynamic cost management of projects and allows quick responses to design changes.
(2) Accessing the BIM Software Database via ODBC
A BIM model essentially functions as an open database containing comprehensive building information. By using ODBC, it is possible to access geometric attribute parameters of components within the BIM model, extract necessary data, and calculate accurate quantities and costs according to predefined quantity and budgeting rules.
The ODBC database stores all component information from the BIM model, and SQL queries can be used to swiftly retrieve data needed for cost budgeting. However, to use this method effectively, a clear understanding of the BIM database structure is essential.
(3) Using BIM Software’s Built-in Automatic Quantity Calculation
Most BIM design software includes features to automatically calculate engineering quantities and export the results into specific file formats, such as Excel spreadsheets, where quantities can be summarized and analyzed.
This method is user-friendly and can significantly improve the efficiency of quantity calculation and cost budgeting, reducing the workload on estimating personnel. However, it requires a standardized BIM modeling process with clearly defined model components to ensure the quantities align with national standards, such as China’s bill of quantities and pricing regulations, guaranteeing accurate results.
After obtaining the quantities, cost budgeting still needs to be performed manually or with dedicated cost budgeting software.
Each of the three methods for quantity calculation and cost estimation has its own advantages and limitations. Selecting the most suitable method depending on functional needs and user preferences can maximize BIM’s value and enhance project management efficiency.
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