1. Why quantities are the centre of gravity
The description in professional sources is unambiguous, and one part of it matters especially. It concerns where the quantities come from.
Working through the design and drawings and calculating the quantities of work is time-consuming and demands precision and experience. The larger and more complex the project, the more time it takes and the more calculation errors arise.
The number of errors therefore grows with the size of the project, and faster than linearly. Quantity take-off is most risky precisely on large projects, and that is where a common schedule is worth most.
2. Where errors come from
Four sources, all structural, and they are handled differently. Some sit in the design, others do not.
| Source of error | Character |
|---|---|
| Misreading the drawing | a dimension or detail misunderstood |
| Omission | an element forgotten entirely |
| Double counting | the same element belongs to two lines |
| Different measurement rule | the same element measured in different ways |
The second is the most expensive, because an omission does not show in a tender, as covered by the article on the absence of structure. The fourth is the only one an agreement removes entirely, as covered by the article on measurement rules.
3. What determines quantity besides the drawing
Three things are not visible on the drawing, which explains why quantity take-off cannot be fully automated. They have to be assessed separately.
The choice of technology, since the same wall can be built in several ways and material consumption differs. The material consumption norm, for which professional sources cite as an example how many screws per square metre must be allowed for when fixing plasterboard. And waste and allowance, which depend on the material and on how the work is organised.
The second is an important distinction: the drawing gives the area but not the number of fixings. According to professional sources budgeting requires knowledge of technology and materials and its inclusion in the price, so quantity take-off is not a purely geometric task.
4. What happens when quantities are wrong
Three scenarios whose consequences differ considerably. The difference lies in who measures.
| Situation | Consequence |
|---|---|
| The quantity is too low and the tenderer notices | they add a risk allowance or make a note |
| The quantity is too low and the tenderer does not notice | the shortfall appears during construction as additional work |
| The quantity is too high | the client pays for work not done, where the contract is lump sum |
The second is the most common and the most expensive. The third depends entirely on who is responsible for the quantities, as covered by the article on requiring a structured tender, and where responsibility has not been agreed, it is settled by dispute, which is the most expensive route.
5. Why this matters particularly in Estonia
One observation about how the market is organised, and it has a competitive effect. Smaller companies are left out.
According to professional sources, larger construction companies use software solutions to simplify and speed up quantity calculation, but according to the same source most construction companies work classically by hand. Smaller ones calculate by hand.
The time and error risk of quantity take-off are therefore unevenly distributed across the market: a larger company can tender faster and more precisely. Providing a common schedule of quantities levels that difference, which opens the procurement to smaller tenderers as well.
Summary and four practical rules
Calculating quantities is time-consuming, demands precision and experience, and the number of errors grows with the size of the project faster than linearly. Errors come from four sources, of which omission is the most expensive because it does not show in a tender, and a difference in measurement rule is the only one an agreement removes entirely. Quantity does not follow from the drawing alone: the choice of technology, the material consumption norm, and waste and allowance are equally decisive.
Four rules: provide a common schedule of quantities, which levels an unequal position between tenderers. Agree the measurement rules, since that is the only fully removable source of error. Decide who is responsible for the quantities before asking for tenders. Allow for the fact that the drawing gives the area, not the material consumption.
This article offers professional orientation as at the date of verification. It replaces neither a quotation nor the assessment of a competent specialist.