Work quantity
Work quantity answers "how much has to be done?" for each item: how many cubic meters of excavation, how many square meters of wall, how many tonnes of reinforcing steel. Every item in the bill of quantities has an associated quantity and its own unit of measure, obtained by taking the measurements off the project drawings.
It is different from the unit price: the quantity is how much there is to do, while the unit price is the cost per unit. The cost estimate is born from multiplying, item by item, the quantity by its unit price and adding up every amount. That is why a badly measured quantity translates directly into a cost overrun or a material shortfall.
Quantities are backed up by the measurement sheet: the backup calculation with the dimensions taken from the drawings (length × width × height, areas, counts) that supports each figure. On site, the estimated quantity is compared against the quantity actually built to measure physical progress and approve progress billings.
In public works, the bill of quantities issued with the tender provides the quantities the contractor must verify; differences between what was measured and what is actually built are settled with measurement sheets and, where applicable, with extra or adjustment items.
Example
For a 10 m × 8 m slab that is 0.12 m thick, the work quantity for the item "structural concrete in slab" is 10 × 8 × 0.12 = 9.6 m³. At a unit price of $3,500/m³, the amount for that item is 9.6 × $3,500 = $33,600.
| Material | Unit | Quantity |
|---|---|---|
| Concrete f'c=250 | m³ | 148.5 |
| Rebar | ton | 12.4 |
| Standard formwork | m² | 620 |
| Block wall | m² | 385 |
| Concrete slab-on-grade | m² | 210 |
Frequently asked questions
How is work quantity calculated?
You take off each item from the drawings, measuring length, width, height, areas or pieces according to its unit, and document it in a measurement sheet. The sum of those measurements is the quantity of the item in its unit (m², m³, lm, tonne, each).
What is the difference between work quantity and quantity takeoff?
The quantity takeoff is the process of measuring and pulling the amounts off the drawings; the work quantity is the result — the specific quantity of each item that the takeoff produces.
Why does measuring work quantity accurately matter?
Because the quantity multiplies the unit price in the estimate: an error in the amount turns immediately into a cost overrun, a material shortfall or delays, and it also creates discrepancies when billing progress.