How to avoid errors when calculating engineering quantities?

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How to avoid mistakes in calculating quantities: To prevent omissions and reduce duplicate calculations, quantities should be computed in a systematic order, step by step. Below are the various sequences commonly used for calculating quantities in civil engineering projects. 1 Calculate in accordance with the construction sequence: the volume of work is determined by following the order in which the tasks are carried out, that is, by calculating the quantities for tasks such as site leveling, digging trenches, laying foundation slabs, constructing brick and stone foundations, backfilling soil, building walls, installing doors and windows, laying reinforced concrete floors, carrying out roof waterproofing, plastering exterior walls, constructing floor surfaces, plastering interior walls, applying plasters, and painting. 2 Calculate according to the prescribed sequence: Determine the quantity of work by following the order in which the various elements are listed in the local specifications, starting from the first item in the first section of those specifications. By referring to the construction drawings, whenever an item listed in the specifications appears in the drawings, the quantity of work is calculated using the rules applicable to that particular section. For items listed in the quota that are not present in the construction drawings, they should be ignored and the next item should be considered. If an item exists whose calculation values are related to those of other items, then that item should be listed first; its quantity will be calculated after the quantities of the related items have been determined. For example, in the case of wall construction, this task falls under the fourth section of the specifications. The volume of work for wall construction is calculated as: (length of the wall × height – area of door and window openings) × wall thickness – volume occupied by concrete and reinforced concrete components embedded in the wall + volume of protrusions and attached flue components. At this point, the wall construction tasks can be listed first; the calculation of the volume of work for these tasks can be postponed. Once the calculations for the concrete and reinforced concrete works in Section 5, as well as the window works in Section 6, are completed, those calculation results can be used to determine the volume of work required for wall construction. This method of arranging and calculating the volume of work according to fixed quotas can effectively prevent beginners from missing or double-counting tasks. 3 Calculate in a custom order as per the drawing. (1) Calculate in a clockwise direction: Starting from the upper-left corner of the plan, calculate sequentially in a clockwise manner. This method is applicable to the calculation of quantities for exterior walls, exterior wall foundations, trenches dug around exterior walls, floor surfaces, ceilings, and interior decorations. (2) Calculate in the order of horizontal first then vertical, top first then bottom, left first then right, by sequentially processing the horizontal and vertical directions on the plan from left to right or from top to bottom. This method is applicable to the calculation of quantities for interior walls, grooves cut in interior walls, interior wall foundations, and interior wall decorations. (3) Calculate and mark according to the sequence of component and fitting numbers shown on the drawings. Number each type of component and fitting—such as columns, beams, slabs, etc.—and then sequentially number the columns as Z1, Z2, Z3, Z4… ； Component numbers such as beams L1, L2, L3..., and plates B1, B2, B3... are calculated in sequence. (4) Based on the sequence of axis numbers indicated on the plan, for complex projects, when calculating walls, columns, and interior and exterior plastering, relying solely on the aforementioned sequence may result in duplicates or omissions. In such cases, it is possible to carry out the calculations according to the order of the axes shown on the drawings, indicating the respective locations with axis numbers. For example, an exterior wall located on axis A, with an axis length of ①～②, can be denoted as A:①～②. This method is applicable to the calculation of work quantities for trenching in interior and exterior walls, interior and exterior wall foundations, interior and exterior wall masonry, and interior and exterior wall decorations. It is recommended to list items in the order of schedule numbers or quota numbers, which helps prevent any items from being omitted. When calculating, first determine which parts can be referenced by other parts; calculate those that are referenced most often first. Some small tips for calculating quantities: drawings follow certain patterns. In the process of preparing a budget, the key step is to understand the drawings; in other words, one drawing is processed at a time. Once a drawing has been processed, it is set aside, and once all the drawings have been processed, it means the drawings have been fully understood and the budget preparation is complete. Therefore, when making a budget, one must be able to read drawings and master a certain sequence for doing so. Firstly, there are several principles for creating budgets based on visual analysis: 1. Look at only one drawing at a time, and try not to look at the same drawing twice; 2. Control the overall amount and make minor adjustments. The budget is determined by controlling the total amount, with further modifications made as the analysis of the drawings progresses. 3. First independent, then overall – the main idea is to calculate those elements that are independent and do not affect each other first, and then to deal with those elements that involve complex deduction relationships. 4. In terms of the order of reading the drawings: first the underground parts, then the above-ground parts ； Structure first, then construction ； Indoors first, then outdoors ； First the main structure, then the roof, and so on. Secondly, based on the aforementioned principles, the diagram is divided into five parts: underground, main structure, main building, roof, and miscellaneous outdoor elements. For each section, determine what needs to be calculated; based on the prescribed sub-items and calculation rules, identify what is required until one is able to accurately compute the quantity of work involved. In fact, it’s not called reading drawings; rather, it involves calculating the quantity of work while looking at the drawings, and once the quantity of work has been calculated, the drawings have been fully understood. Finally, summarize according to the deduction relationships required by the calculation rules, and read through the entire diagram to check for any missed calculations, duplicate calculations, calculation errors, etc. It is best to install the system by starting from the larger end and working towards the smaller end, or from the smaller diameter to the larger one. At the same time, all attachments of the same caliber are listed together. Practical work experience: 1. Good ability to interpret drawings. A good ability to interpret drawings requires the ability to quickly form a spatial impression of components and buildings. It is possible to quickly find the required data through multiple drawings, identify contradictions and errors in them, and visualize the structure of each detail in one’s mind, etc. The methods of representing structural construction drawings have evolved from the traditional separate-style representation to the beam and column tables used in South China, and further to the current flat-method representation. There are various ways of presenting such drawings, and design institutes also have some conventional methods of representation. 2. Thoroughly understand the work procedures and details of the quotas; when studying the drawings of various specialties, it is necessary to stay aware of the designers’ intentions and the content conveyed in the drawings, as well as being informed of any design changes that have taken place prior to construction. Fully master the work procedures for quotas and the contents included in sub-items. Only in this way can we accurately break down the budget items, calculate the corresponding quantities of work, and appropriately apply unit prices, thereby preventing errors such as omissions, double-counting, or incorrect application of prices. 3. Make an overall plan for calculating the quantities: There should be a clear approach to determining the quantities, deciding which parts to calculate first and which later. By making an overall plan for this calculation, efficiency can be improved, which helps save a great deal of time and effort. For example, using the length of the exterior wall’s center line as a basis, it is possible to calculate the quantities related to the various sub-projects. 4. Thorough understanding of the rules for calculating quantities: There are clear rules for calculating quantities, and therefore it is necessary to have a thorough understanding of these rules. In the actual process of all parties verifying the quantity data for the project, disputes often arise, mostly due to different understandings of the calculation rules. To understand the calculation rules, it is necessary to take into account the drawings, the characteristics of construction projects, as well as an understanding of the construction process. The provisions regarding calculation rules need to be carefully considered; for example, the final floor area of a single-story building, regardless of its height, is calculated based on the horizontal area of the structure’s exterior walls. However, when no chamfer is specified in the design, its floor area is calculated based on the horizontal area of the outer exterior wall. 5. Patience and meticulousness: The calculation of engineering quantities requires patience and meticulousness; no carelessness is allowed. Moreover, making corrections after an error occurs is rather cumbersome. For example, when calculating the foundation cushion, the calculation rules specify that it should be calculated based on its actual volume. When the width of the working area changes, the center line of the exterior walls and the net length of the interior walls will change, which is different from the case with soilwork. Some cost estimators often use the values of the center line of the exterior wall and the net length of the interior wall, which have already been determined for earthwork calculations, to compute the volume of the foundation cushion layer, resulting in errors in the construction of such a layer. 6. Good working habits, such as customary ways of expressing formulas, methods for representing intermediate calculation data, and ways of making annotations on drawings, etc. Because the calculation data needs to be verified with relevant parties, and one also needs to check historical projects and so on. 7. Master advanced tool technologies. Nowadays, computers are widely used, and they play a significant role in tasks involving data consolidation and calculation. They help reduce the workload of budgeting staff while also minimizing errors resulting from manual calculations. During the calculation process, it is required that we strive to improve the accuracy of the input of raw data. For example, when entering the range for a summation formula, it is common to accidentally omit one or several terms. The order of calculating the quantities of work should generally be determined based on one’s own experience and habits, rather than following someone else’s methods. The key is to ensure that no items are missed while also striving to improve the speed of calculation.