Last edited 04 Sep 2020

Approximate bill of quantities

An approximate bill of quantities (sometimes referred to as a notional bill of quantities or provisional bill of quantities) can be used on projects where it is not possible to prepare a firm bill of quantities at the time of tendering.

Generally, the design will be relatively complete, but there is either insufficient time or information to determine the exact quantities and so a conventional bill of quantities cannot be prepared.

Tendering on the basis of an approximate bill of quantities can allow early selection of the contractor and so an early start on site. However, the approximate nature of the bill of quantities will tend to result in more variations during construction and so less price certainty when the investment decision is made. This means that even if it is not possible to determine exact quantities, it is sensible to try to ensure quantities are as accurate as possible.

Some contracts allow for re-measurement of approximate quantities (for example, this is common on cut-and-fill on roadworks). Here, quantities are simply revised and payments made accordingly without the need to instruct a variation.

If an approximate quantity turns out not to have been a realistic estimate of the quantity actually required, this may constitute a relevant event, giving rise to claims for an extension of time and loss and expense.

Approximate bills of quantities can also be used during the design process as a tool for controlling design costs (see approximate quantities cost plan below). They are then sometimes included in the tender documents as a guide with a caveat stating that responsibility for measuring quantities lies with the contractor, and drawings and specifications take priority over any description in the approximate bills.

An approximate quantities cost plan is, in effect, a priced approximate bill of quantities. It is a development of the elemental cost plan, but unlike the elemental cost plan (in which the cost of elements is broken down from the overall construction cost, based on the experience of the cost consultant and known costs of similar completed projects) the approximate quantities cost plan is a first attempt to measure defined quantities from drawings.

It presents a more accurate picture of where costs are distributed, in particular it draws to the attention of designers those elements of the design that are standard and those that are not - and as a consequence may be more expensive. The approximate quantities cost plan should form a solid base for an effective value engineering exercise. From the point that the approximate quantities cost plan has been approved, cost control can be introduced by treating changes as if they are variations.

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