Quantity takeoff

The same wall yields different defensible quantities depending on what the takeoff is for. A bid wants the net measured quantity. Procurement wants gross: net plus waste, laps, and over-order, rounded up to supply increments. Progress billing wants the work in place, by the contract's named method of measurement. Scope reporting wants gross area figures such as gross internal area or a BOMA or IPMS boundary, a real-estate figure not a material quantity.

On re-measurement contracts the payment quantity is the actual work measured, not the estimated bill. The FIDIC Red Book is a re-measurement contract whose Clause 12 re-measures the bill of quantities, while its Yellow and Silver books are lump sum, and NEC4 main Options B and D are the priced and target bill-of-quantities options.

The governing principle of every standard method is that the measured quantity is the work net, as fixed in its final position: the actual finished solid, surface, or length, not the material bought or the pre-cut stock length. The net quantity already includes the rule-deemed material for laps, joints, and seams where a work section directs it, so you do not then add laps as free-floating waste. Two companions go with the rule: curved work is measured on the centerline of the material, and dimensions are stated in the order length, width, height as finished sizes.

Every item is taken off in the unit by which it is bought, installed, and priced, on a ladder from the most reliable to the most derived. Count (number or each) suits doors and fixtures. Linear (metres or linear feet) covers pipe, trim, and fence. Area (square metres or square feet) covers finishes, formwork, and cladding. Volume (cubic metres or cubic yards) covers concrete and earthwork. Weight (tonnes or pounds) covers rebar and steel, derived from length times section weight. Choosing the wrong output type, such as pricing pipe by count, is a category error. For repeated work, you measure one condition once and multiply by the count, tracing only unique items.

Quantities are reported in the region's unit system. Metric (metres, square metres, cubic metres, tonnes) is used under NRM2, CESMM4, ANZSMM, DIN, and ICMS. US customary (linear feet, square feet, square yards, cubic yards, pounds, tons) applies in the United States, which also uses squares of 100 square feet for roofing and board-feet for lumber. Canada is mixed: metric drawings with imperial materials.

NRM2 pins rounding precisely: dimensions to the nearest 10 mm, where 5 mm and over rounds up; quantities to the nearest whole number, except tonnes, which go to two decimal places; and a quantity smaller than one unit given as one unit. US imperial rounding is a convention: dimensions up to the next whole foot, and concrete to about a quarter of a cubic yard. Direction depends on purpose: nearest for a bid, but up for a material order.

Deductions follow one NRM2 philosophy with two halves. An internal void is only deducted once it is above a minimum size, because the labour of working around a small one offsets the material saved. A void at the boundary is always deducted whatever its size, because that is where the work stops.

The threshold for the internal half is specific to the trade and region. Under NRM2, finishes are deducted above 1.00 square metre, masonry above 0.50 square metre, and in-situ concrete above 0.05 cubic metre. German concrete deducts openings larger than 0.5 cubic metre under VOB/C DIN 18331. In the United States, paint follows a roughly 100 square foot threshold from the Painting Contractors Association, and drywall follows a convention of around one full sheet.

A length-versus-area trap follows: the same opening is deducted from area once above the threshold, but left in the linear length, since the plates or track still run through it. Baseboard is the exception, lifting across a doorway.

Net is the standard-method measured quantity with rule-based deductions applied, the basis for bidding, billing, and installation. Gross is the un-deducted envelope that keeps internal walls and columns in, which boundary standards like BOMA and IPMS deliberately define as gross. Mixing them is a classic error, such as reporting gross area to a subcontractor who prices net.

A waste, scrap, lap, or over-order factor belongs to the material order, not to the measured boundary. You measure net, then multiply by one plus the waste factor only to work out how much to buy. Baking waste into the boundary corrupts the audit trail and double-counts when downstream pricing also adds waste. NRM2 keeps general waste in the unit rate or risk allowance, so the principle is codified while the percentages are conventions applied only at ordering.

A two-dimensional plan understates anything that runs out of the plane, so sloped work needs true or developed quantities: the plan area times the slope factor, the square root of the rise over run squared plus one. You also add the vertical legs the plan hides (risers, drops to device height, and slab stub-ups), the most common cause of under-measurement in mechanical and plumbing work.

Heights come off sections and elevations; runs and areas come off plans. Drawing sets are organised by discipline series (the leading letter) and sheet type (the digit), as codified by the US National CAD Standard: C for Civil, S for Structural, A for Architectural, P for Plumbing, M for Mechanical, and E for Electrical, with digits 1 for plans, 3 for sections, 5 for details, and 6 for schedules. UK and European work uses BS 1192 and ISO 19650. Figured dimensions govern over anything scaled; the schedule is authoritative for ordering, the plan for location. Recalibrate scale on every sheet, since a doubling of scale error quadruples a measured area.

Precision is bounded by how complete the design is. AACE and ASTM E2516 classify estimates from Class 5 (a concept-stage parametric estimate with the widest accuracy band) down to Class 1 (a full bid or tender takeoff with the tightest band). A takeoff on a schematic set is inherently approximate and should not be presented as a Class 1 number. For scope that cannot yet be measured, the standards carry formal provisional quantities, provisional sums, and dayworks, which should be labelled provisional rather than firm.

A quantity is only useful if it can be re-measured, so each one needs a trail: the source sheet, the boundary rule used, and the build-up arithmetic. Self-checks reconcile net to gross and counted plan symbols against the schedules. Exayard reads the plan set, applies these rules, and records the boundary and build-up behind each quantity so it can be re-measured and defended.