Quantity takeoff methods and workflow

Quantity takeoff is the measurement of the work shown on drawings and described in specifications. It is the foundation of every detailed estimate: a perfect unit price multiplied by a wrong quantity is a wrong number. Takeoff is also where most estimating time goes, and where most errors start. CON-120 taught you to read drawings and CON-130 the arithmetic of areas and volumes; this lesson turns those skills into a disciplined workflow that produces complete, checkable quantities under bid-day pressure.

Preparing to take off

Good takeoff begins before any measuring. The estimator first reviews the whole bid package to understand the project and to plan the work.

• Read the instructions to bidders, bid form and addenda list, so you know what is being priced, how alternates and unit prices must be shown and when questions must be asked.
• Scan every drawing sheet and the specification table of contents, noting the systems used, unusual items and any work shown on one discipline's drawings that another trade will perform.
• Decide what will be self-performed and what will be subcontracted. The firm takes off its own work in detail and usually does a check takeoff of major subcontracted work.
• Set up the estimate structure, cost codes and takeoff sheets or software folders before measuring, so every quantity has a place to go.
• Confirm the scale of every sheet you will measure from, and note any sheets marked not to scale.

Questions found during this review go to the designer through the bidding procedure, usually as written requests for clarification before a stated deadline. Answers come back as addenda that bind every bidder, which is why an estimator must confirm that every addendum has been received and incorporated before submitting a price.

The four kinds of measurement

Almost every item in an estimate is measured in one of four ways, matched to how the work is built and bought.

• Count: items installed individually, such as doors, light fixtures, plumbing fixtures, anchor bolts and piles. Count on plans, check against schedules, and mark each item as you count it.
• Linear: items measured along their length, such as strip footings, curbs, base, handrail, pipe, conduit and trench. Measure along the centreline for items with thickness, such as walls and footings, and adjust corners consistently.
• Area: items measured by surface, such as slabs, roofing, drywall, painting, flooring and formwork contact area. Decide the deduction rule for openings before you start.
• Volume: items measured in three dimensions, such as concrete, excavation, backfill and gravel. Measure as dimensions in place, then convert to the purchase unit.

Many items are measured one way and priced another. A footing is taken off by length but its concrete is bought by volume, its formwork by contact area and its reinforcing by mass or weight. A good takeoff therefore records the dimensions behind each quantity, such as length, width and depth, so that every derived quantity can be calculated from the same measurement.

Recording takeoff

Whether on paper or in software, takeoff must be recorded so that someone else can follow it. The traditional takeoff sheet has columns for the item description, the drawing reference, the number of times the item occurs, the dimensions and the resulting quantity, with totals carried to a summary sheet. Software replaces the columns with measured objects on the drawing, but the principles are the same.

A few habits make takeoff reliable. Work in a fixed order, such as left to right and top to bottom on each sheet, and by grid line on structural plans. Mark every item on the drawing as you take it off, using one colour per item, so you can see at a glance what has been missed. Keep each item's quantity as calculated, without rounding, until the summary; round only the purchase quantity. Use the same units throughout one item. Write down assumptions, such as an unclear dimension you scaled, beside the quantity.

Canadian drawings are usually in millimetres and metres, but many products are still bought in imperial sizes: lumber in nominal inches and feet, plywood and drywall in 1220 mm × 2440 mm sheets (4 ft × 8 ft), and some pipe in inch sizes. The takeoff should be in the drawing units, with conversion to the purchase unit done once, in the pricing.

Digital takeoff from PDF drawings

Most takeoff today is done on screen. Digital takeoff software displays PDF or image drawings, lets the estimator set the scale for each sheet, and measures lines, areas and counts with the mouse, linking each measurement to an estimate item. Benefits include speed, colour-coded marking of what has been measured, automatic recalculation when an item is redrawn, and overlay comparison of revised drawings, which highlights changes issued by addendum. Takeoff tools also export quantities to estimating software or spreadsheets.

The main risk of digital takeoff is scale. A PDF can be printed or scanned at any size, so the graphic scale or a known dimension must be used to calibrate each sheet. Estimators calibrate on the longest dimension string they can find, then check a second known dimension in the other direction. A sheet that has been stretched during scanning can have different scales horizontally and vertically, which a single calibration will not catch.

Typical floors, repetition and multipliers

Buildings repeat. Apartment and office floors are often identical, and the same room, door or wall type appears many times. Estimators save time by measuring a typical unit once and multiplying, but multipliers are also a classic source of error, because the typical floor is rarely exactly typical. The ground floor may have a lobby instead of suites, the top floor may have mechanical rooms, and one floor may be mirrored.

Checking quantities

Every takeoff should be checked before it is priced, and the check should use a different method from the takeoff, because repeating the same steps repeats the same mistakes. Common checks include the following.

• Independent recalculation: measure the item again a different way, such as a slab as gross area minus openings instead of a sum of rectangles.
• Ratios: compare quantities with the floor area and with similar projects, such as reinforcing in kilograms per cubic metre of concrete or pounds per cubic yard, drywall area per unit of floor area, or doors per suite.
• Schedules: compare counts with door, window, finish and fixture schedules, and resolve every difference.
• Visual review: look at the marked-up drawings for unmarked items, especially on sheets from other disciplines and in details and sections.
• Peer review: on large bids, a second estimator reviews the major quantities before pricing.

Managing addenda and revisions

Drawings change during bidding. Addenda may add sheets, replace sheets, or change a single dimension in a note. Every change must be found and taken off. Digital overlay comparison, which shows the old and new sheets in contrasting tints, makes changes visible, but written addenda changes to specifications must be read line by line. The estimator keeps an addenda log listing each addendum, the date received, the items affected and the estimate lines changed, and confirms on the bid form that all addenda were received.

After contract award, the same discipline applies to revisions and change orders: the estimator or quantity surveyor measures the difference between the old and new design, prices it and records the basis. Clean takeoff records from bidding make change pricing much faster, because the original quantities and assumptions are already documented.