Last edited 19 Feb 2021

Firm bill of quantities

A bill of quantities (BoQ) is a document prepared by a cost consultant that provides project-specific measured quantities of the items of work identified by the drawings and specifications in the tender documentation. The quantities may be measured in number, length, area, volume, weight or time. A bill of quantities is issued to tenderers for them to prepare a price for carrying out the works.

The more precisely the work in a bill of quantities can be measured and described (i.e. the ‘firmer’ it is) the more accurate tenderersprices should be, the easier it will be to control costs and the fewer variations will be necessary. The process of identifying elements of construction works that can be measured and priced is known as 'taking off'.

A firm bill of quantities can be prepared when the design is complete, a detailed specification has been prepared and quantities can be accurately calculated. If there were no changes to the project requirements following the preparation of a firm bill of quantities, then the tenderer’s priced bill of quantities would be the same as the final cost of the contract. In practice of course there are always changes.

Where it is not possible to prepare a firm bill of quantities at the time of tendering, an approximate bill of quantities (or notional bill of quantities) might be prepared. This might be necessary, for example, if the design is relatively complete, but exact quantities are not yet known. However, this will tend to result in more variations during construction and so less price certainty when the investment decision is made.

Approximate bills of quantities can also be used during the design process as a tool for controlling design development.

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