Quantity takeoff errors are common, costly, and largely preventable. Most estimation disputes on Ghanaian construction projects have a measurement mistake somewhere in the chain — either in the original BOQ or in the contractor's priced document.
This guide covers the nine most frequent errors Ghanaian QSs make during takeoff, why each happens, and what the correct approach is.
1. Measuring in Bulk Instead of Net
The error: Measuring excavation in its disturbed (bulked) state instead of the net in-place volume from the drawings.
Why it happens: QSs instinctively think about what the contractor actually moves (which is more), not what the drawings specify.
Correct approach: Measure net volumes from the drawings. The bulkage factor (typically 20–30% for normal soil) is a pricing adjustment in your rates, not a measurement adjustment to your quantities.
2. Double Counting Across Work Sections
The error: Including the same quantity in two sections — for example, measuring blockwork area in the walling section and again as part of a composite item in the finishes section.
Why it happens: Poor section structure or lack of cross-referencing during takeoff.
Correct approach: Define section boundaries clearly before taking off. Use a check sheet to confirm each element appears in exactly one section.
3. Ignoring Opening Deductions
The error: Measuring blockwork or plastering as gross area without deducting door and window openings.
Why it happens: Speed during takeoff, or assuming the deductions are "small enough to ignore."
Correct approach: Per SMM7 convention, deduct openings over 0.5 m² for blockwork and over 0.1 m² for plastering. Small openings are ignored; large ones must be deducted. Ignoring a 2.4 m × 1.2 m window is a significant error in a heavily-fenestrated building.
4. Using Finished Dimensions for Concrete Where Formwork Margin is Needed
The error: Measuring concrete net volume and forgetting that the formwork must account for pour pressure and tolerance — but then separately over-measuring concrete volume to compensate.
Correct approach: Measure concrete net. Measure formwork as a separate item (superficial area of contact face). Waste is a pricing allowance on the concrete rate, not a quantity addition.
5. Failing to Segregate Excavation by Depth
The error: Treating all excavation as a single item regardless of depth.
Why it matters: Excavation cost changes with depth — deeper cuts require different plant, longer cycle times, possible strutting, and dewatering. A flat rate across all depths underestimates deep work and overestimates shallow work.
Correct approach: Segregate excavation into depth bands (e.g. 0–0.25m, 0.25–1.0m, 1.0–2.0m, exceeding 2.0m). Apply appropriate rates to each band.
6. Approximating Reinforcement Instead of Scheduling It
The error: Using a "per m³ concrete" reinforcement factor (e.g. 100 kg/m³) instead of taking off from a bar bending schedule.
Why it is risky: Lightly reinforced slab vs heavily reinforced beam can differ by a factor of 4 in reinforcement content. A blanket factor on a mixed structure produces wildly inaccurate totals.
Correct approach: For tender BOQs, use approximate quantities if no bending schedule is available, but clearly flag them as provisional. For contract BOQs, use the actual bending schedule.
7. Omitting Builder's Work in Connection
The error: Not including holes, chases, plinths, and fixings required for services (M&E, plumbing).
Why it matters: In Ghana, M&E subcontracts often exclude builder's work, leaving a gap in the main BOQ. The main contractor then claims it as a variation.
Correct approach: Include a builder's work in connection section, even if approximated, to flag that these costs exist and will be priced by someone.
8. Not Checking the Drawing Revision Used
The error: Taking off from a superseded drawing issue.
Why it is common in Ghana: Drawing management on many project sites is informal. Architects issue revisions by email without formal drawing registers.
Correct approach: Record the drawing number and revision used for every takeoff sheet. Request a drawing register from the architect before starting. If revision control is absent, document your assumption explicitly.
9. Treating Provisional Sums as Accurate Estimates
The error: Including a provisional sum for undefined work and treating it as a firm cost when reporting project budget.
Correct approach: Provisional sums are contractual placeholders for scope that has not yet been fully designed or specified. They are not estimates — they are intentional gaps. Budget reports should flag them explicitly and estimate the confidence range for each one.
A BOQ with clean quantities and honest provisional sums is more valuable than a BOQ with fabricated certainty. The contractor, client, and their lawyers all know the difference when it matters.
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