A quantity take-off provides a bill of all the materials necessary for the completion of the project. Each material has a quantity required for the project and the estimator should compile the list of costs for the related materials. It is also called the quantity survey and the compiled list is called Bill of materials.
The estimator must review the three documents before preparing a bill:
Drawings – Complete and detailed, including plans, elevations, sections, and other details.
Specifications – Details about the nature, quality, and class of work, materials to be used, and quality of the material, their proportions, and method of preparation are required.
Tender notes – Outlining exceptions, such as inclusion of working space while calculating excavation volume.
Quantities should be shown in standard units of measure and should be consistent with design units. Various types of calculation involved are:
Volume = Length × Width × (Height or Thickness)
Area = Length × Width
Quantity = Length
Quantity = Number of Units.
Quantity = Weight.
Importance of Quantity Takeoff :
Quantity Take off is required in inviting tenders for the works for competitive bidding
Quantity Take off is required to estimate the quantities of the various materials required and the labor involved for satisfactory completion of a construction project
Quantity Take off is required to calculate payments to the contractor for actual measurements of the completed part
Quantity Take off is required in insurance, legal, and dispute matters
Planning the work
An estimator must thoroughly understand the project scope of work, the bid ability, constructability, and aspects of the project estimate.
As the estimator performs the quantity take off the materials, equipment, and labor tasks must be divided into bill of materials.
CPWD guide provides a list of items commonly used in the bidding process.
The detail to which the quantities are prepared for each task is dependent on the level of design detail.
Quantity calculations beyond design details are often necessary to determine a reasonable price to complete the overall scope of work for the cost estimate.
Project notes will be added at the appropriate level in the estimate to explain the basis for the quantity calculations, to clearly show contingencies, and to note quantities determined by cost engineering judgment that will be reconciled upon design refinement.
Guidelines for preparing an efficient quantity take off
The estimate is much more efficient when standard estimating guidelines are established and followed. This provides an advantage enough when a single estimator is preparing a specific estimate but is even more important when multiple estimators are working on the same project. By keeping a uniform and consistent take-off process, the chance of error or omission is greatly reduced, and productivity is increased. Multiple estimators will find it easier to work on the same project; and if a personnel change takes place, it is much easier for a new estimator to pick up.
Use of standard forms for the orderly sequence of item descriptions, dimensions, quantities, pricing information, etc.
Abbreviate (consistently) whenever possible.
Be consistent when listing dimensions in sequence length by breadth (width) by height).
Use dimensions as used in design drawings.
When possible, add up the printed dimensions for a given item.
Take advantage of design symmetry or repetition. e.g. plastering quantity is the same as Painting.
Convert imperial dimensions (feet/inch) to decimal equivalents.
Avoid manual calculations. Preferably use excel for all calculations.
Do not convert the units until the final quantities are obtained.
Items should be measured/converted to the same units consistently throughout the take-off.
Mark the drawings as quantities are taken off. Use different colors to identify various types of components or items, as well as to identify items on hold, etc.
Keep similar items together, and different items separate.
Organize the take-off to match the control structure and format of the estimate.
Identify drawing numbers, section numbers, etc. on the take-off forms to aid in future checking for completeness, and for incorporating late changes later on.
Be alert for notes shown on drawings, changes in the scale used on different drawings, drawings that are reduced from the original size, discrepancies between drawings and specifications, changes in elevation that may not be obvious, etc.
Be careful to quantify all labor operations that may not have a material component.
Conclusion: After the take-off is completed, the quantities can be extended, consolidated, and priced. If a procurement department or other resources will be utilized to investigate certain pricing (major equipment, large bulk material purchases, subcontracts, etc.), a listing should be compiled and sent to the appropriate person.