Table of Contents
Learn the Best Method to Produce an Accurate Quantity Takeoff
What Is a Construction Quantity Takeoff?
According to the Dictionary of Construction Terms, a construction quantity takeoff, in theory, is “the estimation of quantities for a contract from plans and drawings which are then recorded in the bill of quantities” (305). In practice, however, a construction quantity takeoff is a term commonly used in the industry to describe one of its most essential functions: the process by which a cost estimator reviews a set of plans during preconstruction in order to “take off” measurements from these plans to forecast construction costs. The term takeoff actually evolved from the phrase “taken off,” which loosely translates to “measured.” Only by taking the information “off” documents can estimators convert information from drawings into a list of items with quantities that can be measured. While performing a quantity takeoff, estimators “take off” information from common contract documents: including architectural drawings, structural engineering drawings, plumbing drawings, site water reticulation and drainage drawings, electrical drawings, and HVAC drawings.
Despite the fact quantity takeoffs are so common in the industry there is still some confusion over what the process entails. For example, many assume a quantity takeoff refers only to estimating materials or that the process simply consists of reviewing a set of project plans and then quantifying information about the physical materials the architect, engineer, or draftsperson specifies to build the project. But a quantity takeoff is actually not the process of estimating materials directly. In fact, according to expert David Pratt, in his detailed analysis of the term in the Fundamentals of Construction Estimating, a quantity takeoff is actually the process of measuring the work of a project in the form of a series of quantified work items, which includes both labor and materials. Again, the work, not the materials.
The confusion regarding quantity takeoff stems from the fact that takeoffs are often referred to in the industry by many names, and these names are used interchangeably even though they can refer to different things:
- Takeoff or take-off
- Quantity take-off
- Materials takeoff
- Construction takeoff
- Material estimating
- Material counts
- Quantity surveying
For example, although materials takeoff and quantity takeoff are most often treated in the industry as identical processes, they’re actually two different processes that should be distinguished from each other.
3 Differences between Materials Takeoff and Quantity Takeoff
A materials takeoff, used to calculate the quantity of materials that needs to be purchased in order to construct a particular item of a project, differs from a quantity takeoff for a cost estimate in three substantive ways:
- In cost estimate quantity takeoffs, measurements are made “net in place” whereas materials takeoffs measure gross quantities.
- A materials takeoff also rarely includes sufficient information for actual pricing. For example, “100 cubic yards of 3000 psi concrete” may be adequate for a materials takeoff, but information about what the concrete is to be used for is required in a cost estimate takeoff.
- Many work items measured in a quantity takeoff do not involve materials at all. A good example is “Hand Troweling,” which only has a labor price associated with it. In this case, what needs to be measured is the plan area of concrete that needs to be trowelled. There is no material associated with it and therefore to consider when creating the takeoff.
For these reasons, when we refer to “takeoff” in this guide, we’ll be specifically referring to the process of quantity takeoff, which measures the work of a project as a series of quantified items.
More importantly, a quantity takeoff is also not an isolated activity, but is just the first of six steps necessary to complete a detailed and accurate project cost estimate:
- Step 1: Takeoff quantities–the work to be performed by a contractor is measured in compliance with standard rules of measurement
- Step 2: Recap quantities–the quantities of work “taken off” are sorted and listed to comply with the CSI MasterFormat or other standard to facilitate the process of pricing
- Step 3: Recap pricing–prices for the required labor, equipment and materials are entered against the quantities to determine the estimated cost of the contractors work
- Step 4: Subcontractors work pricing–prices are obtained from competing subtrades who quote to perform the work of their trades;
- Step 5: General expenses pricing–the costs of the anticipated project overheads are calculated and added to the estimate
- Step 6: Estimate summary–all estimated prices are summarized
The detailed estimating method outlined above is far more likely to produce a price that accurately forecasts the actual costs of building a construction project than just a quantity takeoff, but the quantity takeoff provides the necessary foundation for an accurate work assessment and this accuracy can only be achieved if the project owner provides an estimator with a defined scope of work in the form of drawings and specifications.
How to Do a Quantity Takeoff
As we’ve already noted, a detailed estimate begins with a quantity takeoff. To prepare the takeoff, an estimator has to break down the design shown on the drawings and described in the specifications into predefined activities or work items that correspond to the operations the contractor will perform to complete the work of the project.
The basic takeoff process is as follows:
- Define takeoff scope: An estimator must thoroughly answer the question “What needs to be taken off or measured?” by study plans and specs. If any details are unclear, the estimator should as the architect or owner rather than guestimate or make assumptions.
- Measure each item: Once the scope of the takeoff is understood, the estimator should use the dimensions specified in the plans and specifications to measure each item without scaling drawings unless necessary. Estimators shouldn’t rely on scaled dimensions because sizes are often changed in the design phases and this often results in drawings that are out of scale.
- Record quantities: An estimator then makes detailed references as to which sheet the items were found and where they exist in the building or structure. And finally, the estimator records quantities by including drawing number, detail number, and grid reference in a list.
However, for larger projects, a more comprehensive strategy is necessary to manage the sheer volume of items to measure and count. In these instances, an estimator should divide the project into smaller more manageable parts and then consider one part of the project at a time. The way an estimator chooses to break up a project into manageable pieces depends on the type of project. High rise projects, as one example, are most easily divided into floors or groups of floors. Some projects can be divided into zones, phases or even separate buildings.
Once the project is divided into parts, each part is then further divided into what are called “assemblies,” which are simply components of the work that can be considered separately from other aspects of the project. The estimator will measure every aspect of a given assembly and then move on to the next assembly. Let’s use a perimeter wall as an example. The estimator will takeoff all the items associated with a particular assembly before moving on to the next: (1) the concrete wall, (2) the forms to the side of the wall, (3) the forms to openings and blockouts in the wall, (4) the rubbed finish on the exposed concrete of the wall, and (5) the reinforcing steel of the wall. Measuring by assembly avoids needless repetition and actually speeds up the process because no time is wasted reassessing the component, repeating the dimensions and possibly recalculating these same dimensions several times.
Many cost estimators also maintain a catalog of standard items representing activities that will be encountered on a large variety of projects, but it’s not uncommon to have to take on a new category of work unique to a particular project. The catalog of standard work items is often used as a checklist during the takeoff process, especially by junior estimators to ensure all the general categories of work have been factored into the estimate.
Once the project scope is understood and the project is broken into smaller assemblies, the cost estimator is ready to measure individual items of work. Each item in a construction quantity takeoff is measured according to a set of rules with the object of producing a list of work items and their associated quantities in a format estimators are familiar with. Because a standard format is used, estimators are able to easily review and evaluate the work and then price it accordingly. These measurement requirements collectively amount to a uniform method of measurement that can be shared by estimators, and it’s prudent for estimators to adhere to the method of measurement because price information can only be shared if it relates to work measured by the same method.
To achieve greater efficiency and accuracy, various types of stationary and worksheets are used by estimators for specific takeoff and estimating procedures. We recommend cost estimators use separate worksheets for the takeoff and the recap portion of the cost estimate to make pricing more efficient.
What Is Measured in a Quantity Takeoff and How Is it Measured?
In North America, estimators use two systems of measurement: the English system and the metric system and both have their own set of units. Generally, items of work are measured in the units most appropriate to the type of work involved, and this approach is reflected in the rules of measurement adopted by the estimator or department. Pipe and lumber, as two examples, are usually measured by the unit of length. However, concrete and asphalt will likely be measured by volume. An example using rules of measurement can be demonstrated with the dimension of length: the quantity measured is the length of the item in feet and the final value is written as linear feet (lin. ft.)
Example of Pipe Measured by Length: 6” Dia. ABS drain pipe = 300 lin. Ft. (91m)
Quantity takeoff items are composed of both dimensions and descriptions. Although there are 5 basic categories of units when preparing a detailed estimate, takeoff items are always recorded in terms of three units of measurement: length, width and height. Furthermore, each description for an item of work in a quantity takeoff needs to be detailed enough for the estimator to price the work.
To ensure objectivity and accuracy, all work in the quantity takeoff is measured in “net in place,” which means quantities are calculated using the dimensions on the drawings with no adjustments made for waste and other factors. This is important, as many sources explaining how to do quantity takeoffs frequently tell estimators to make adjustments for waste, which is poor advice and will ultimately reduce takeoff accuracy.
Finally, the takeoff process is usually organized to follow the sequence of construction which often mirrors the order contract drawings and specs are usually presented. However, occasionally an estimator will deviate from this sequence and measure concrete before earthwork requirements or excavation first because that’s how drawings have been presented.
What Is Not Measured?
If a cost estimator wants to avoid mistakes, it’s also important to know what shouldn’t be measured in a construction quantity takeoff. When describing a work item in a quantity takeoff, the estimator shouldn’t mention or measure any of the following items individually because they will be handled later during the pricing phase of the takeoff items:
|Transportation or any other cost associated with the delivery of materials involved||Lapping, cutting or waste of materials|
|Unloading materials||Stripping formwork|
|Hoisting requirements||Form Oil|
|Labor setting, fitting, or fixing in position||Rough hardware|
3 Primary Takeoff Methods: Manual, Digital, and Estimating Service
Traditionally, all takeoffs were performed manually. However, in the last 10 years cost estimating has changed rapidly with the introduction of new technologies. Although technology has increased the speed and accuracy of producing a quantity takeoff, takeoffs created via the use of computer software or other technology still require human operators and interpreters no differently than takeoffs produced manually. While the assumption has always been that there are only two methods for developing a quantity takeoff, the advent of artificial intelligence has challenged that assumption, enabling a new method of producing takeoffs that increases speed and accuracy while also leveraging indispensable insights from trained estimators with years of experience. Moreover, there is no reason an estimator can’t use more than one of these methods for a single project estimate. In fact, many estimators who create digital takeoffs often prepare paper takeoffs before they enter dimensions into a computer.
Here we briefly describe three primary methods for creating a quantity takeoff: manual, digital, and estimating service:
Method 1: Manual
When a construction cost estimator prepares a quantity takeoff without using takeoff software or cost estimation software then they are using the manual method, even if they utilize an excel spreadsheet, word processor, or other software sometime during the process. As we’ve already noted, the manual process at its most basic level involves reviewing the scope of work via contract drawings, reading the plans and specifications, and then taking accurate measurements from those documents to determine the type and amount of work required to build a structure. Specifically, the estimator will review each sheet of the drawings, calculate the quantity of material, and record the amount and unit of measure on the appropriate line item of the estimate. For these reasons, the estimator must be able to read project plans and specifications and be adept at calculating complex mathematical equations. The cost estimator also needs to have good attention to detail to ensure that nothing is missed so the estimate is as accurate as possible.
There are obvious downsides to preparing a quantity takeoff manually, which include a lag time when procuring the physical plans in order to start the takeoff process, the wasted time when having to manually enter measurements onto a paper worksheet or software program, and finally reduced accuracy.
Method 2: Digital
Digitizers: Digitizers are electronic devices that enable the user to take measurements from drawings and input that data directly into a software program. Construction estimators employ two primary types of digitizers: sonic and tablet. Both devices use a pointer or cursor to locate points and lines. With a sonic digitizer, the device emits a sonic code for the cursor which is then identified by two receivers, which can precisely calculate the location of the cursor. With a sonic digitizer, almost any drawing can be scanned regardless of its size or the source it’s placed on. In contrast, with tablet digitizers, physical drawings have to be laid out on top of an electronic tablet, which scans the document and identifies the exact location of the cursor. Once the information is captured by the digitizer, it’s available for processing by sophisticated estimating software, which can quickly calculate measurements. In some cases, the estimating systems can be operated directly from the digitizer, eliminating keyboard entry.
One downside to a tablet digitizer is that due to the enormous size of the drawings needed to be scanned, a cost estimator may need to use a tablet as large as 42” by 60” to ensure all drawing information is accessible at once. Another drawback for both digitizers is that the accuracy of the final quantity takeoff is directly dependent on the accuracy of the drawings provided.
On-screen Takeoff Technology: Similar to digitizers, on-screen takeoff technology digitizes plans and drawings. The major difference with on-screen takeoff tech is that it allows the cost estimator to measure quantities directly from digitally-stored drawings, thus eliminating the need for paper printouts of plans. Digitized drawings can be stored in many widely accessible formats, including BMP, JPG, DWG, DXE, PDF, PIC, and TIF. Similar to sonic and tablet digitizers, on-screen takeoff technology can also be integrated with estimating software for increased efficiency.
On-screen takeoff technology provides many benefits, which include cost savings from eliminating printing as well as time savings by eliminating manual entry of takeoff dimensions. However, one cost of on-screen takeoff technology is that drawings will need to be precisely scaled in order to ensure the final quantity takeoff is accurate.
Takeoff Software: Takeoff software enables estimators to create takeoffs that are completely digital. Construction takeoff software simply enables the estimator to automate many of the time-consuming processes of the quantity takeoff process, including generating materials, performing calculations and streamlining pricing.
However, unlike cost estimating services reviewed below, takeoff software can be expensive and also time-consuming to learn and master.
Method 3: AI-Powered Cost Estimating Services
The third and newest method for developing a quantity takeoff is enhanced cost estimating services, which combines the power of artificial intelligence with experienced estimators to provide the benefits of both manual and digital methods for takeoffs.
While there are a few companies offering cost estimating services, only one company is using machine learning to fundamentally revolutionize how quantity takeoffs are done: 1build. 1build is by far the best takeoff service because it uses next-generation artificial intelligence and deep learning to improve the detail and accuracy of quantity takeoffs. With this revolutionary approach, a builder simply subscribes to the service, uploads plans, and then receives a detailed quantity takeoff or cost estimate.
Once plans are uploaded, estimators with decades of field experience in every construction sector review the plans and leverage complex AI algorithms to accurately count and measure takeoff items. The result is that the construction quantity takeoff is delivered in a fraction of the time it would take to produce either manually or digitally and with greater accuracy. With AI-powered cost estimating services, you can save time, eliminate headaches, and increase your chances of winning bids.
To learn more about how enhanced cost estimating services can help you with your next quantity takeoff sign up for a free trial today.