Technical guideQuantity takeoff
What makes a quantity takeoff traceable
A quantity is only useful if someone else can check it. Four links every line of a takeoff should keep, and how to test your own schedule.
Vương Phạm · Published · 5 min read
A quantity schedule is a set of claims: this much concrete, this much formwork, this much plaster. Each claim is only as useful as the reviewer's ability to check it. A takeoff is traceable when any line can be followed back to the drawing, element and rule that produced it, without redoing the measurement.
The four links
- Source: which drawing, revision and grid location the dimensions came from.
- Element: the named component, such as beam B2 between grids 3 and 4 on level 2.
- Dimensions: the actual values used, with units, not only the result.
- Rule: the measurement rule applied, including deductions for openings and overlaps.
If any link is missing, a reviewer has to reconstruct it. That is where most disputes about quantities begin: two people get different numbers and neither can show why.
A worked line
| Field | Value |
|---|---|
| Source | S-102 rev C, grid 3–4 / level 2 |
| Element | Beam B2 |
| Dimensions | 0.22 m × 0.40 m × 4.60 m clear span |
| Rule | Measure clear span between column faces; slab depth deducted where cast together |
| Result | 0.22 × (0.40 − 0.10) × 4.60 = 0.304 m³ |
Note
Test your own schedule
- Pick five lines at random. Can a colleague find the element on the drawing in under a minute?
- Change one dimension on the drawing. How many cells in the spreadsheet must you edit by hand?
- Ask where a total comes from. Is the answer a formula chain or someone's memory?
Model-based takeoff helps because the links are part of the data rather than a comment in a cell. The same discipline works on paper: name elements, keep dimensions visible and write the rule down once, at the top of the schedule.