Accuracy in Quantity Surveying

Quite often, in the course of finalization of an assignment, clients ask us, “What is the accuracy with which you will provide quantities”. Though not articulated expressly, we understand that the client expects 100% accuracy in Quantity estimation! Obviously, no Quantity Estimator can truthfully claim to provide 100 % accuracy in her deliverable. Our stock answer to this question is “the accuracy will be in proportion to the quality of the drawings & details provided to us”. This answer does not satisfy those who consider them perfectionists.
In one particular case, the client wanted to impose a penalty based on the % error in the quantity estimate, agreeing to pay 100% fees only if the quantities were 100% accurate. Needless to say, we had two choices, either to factor a few % of lost fees in our quote or to opt-out of the bid! We don’t know how the client was to get hold of 100% accurate quantities to assess the final amount payable to us!

Is it really worthwhile to demand 100% accuracy in Quantities?

Before we explore whether quantities can be provided with 100% accuracy, let us examine if this expectation is justified? Quantities are used for any one of the following purposes;

• To prepare the project budget/cost plan
• For finalizing contract price
• For the purpose of bidding
• For the procurement of materials

In the first three cases, the final requirement is cost and not quantity per-se. For any given quantities, the cost may vary widely, depending upon the rates adopted for costing. Rates vary widely and depend on many factors. In competitive bidding, all other factors remaining the same, amount/rates are known to vary by as much as 30-50%.

Similarly, estimation of the quantity of materials depends on factors such as technical specifications, wastage, rolling margin, concrete mix proportions, design changes etc. These factors may cause a variation ranging from 5% to 20%.

If factors other than the quantities cause such a large variation, there is really no justification in demanding an unreasonably high level of accuracy in Quantity estimation. I am reminded of a very witty statement “there is no point in using a Vernier to measure the dimension if you are going to use chalk to mark the piece of wood and use an axe to chop it to the required size”. How apt!!!