What is bill of quantities preparation?
From design information to a priceable scope
Bill of quantities preparation converts drawings, specifications and project requirements into a coordinated list of described and quantified work items. The result is a bill of quantities, or BQ, that enables contractors to price the same scope on a comparable basis.
In Switzerland, this process is known as Devisierung and the document is often called a Devis. The purpose is the same: make scope, quality, unit, quantity and interfaces clear enough for pricing, procurement and later valuation.
What does the preparation involve?
- reviewing drawings, specifications and project constraints
- dividing the works into logical sections and trades
- writing complete and unambiguous item descriptions
- selecting the correct unit and measuring the forecast quantity
- stating execution conditions, inclusions and exclusions
- checking for gaps, duplication and conflicting information
- issuing a coordinated document for pricing
An example item
“Install 160 mm mineral wool insulation boards to external wall, including cutting and system-compatible mechanical fixings; unit m²; quantity 420.” The item identifies the component, material, key dimension, operation, unit and quantity. “Insulate façade as drawing” would rarely provide enough information for dependable comparison.
Standard and project-specific descriptions
Swiss projects often use the NPK catalogue for standardised work descriptions. The structure reduces inconsistent wording and supports digital exchange. It does not remove the need for judgement: selected characteristics, project conditions and interfaces must still reflect the actual design.
Where no suitable standard item exists, a clearly identified free-text item can be added. Standard and bespoke items can work together, provided their units and pricing basis remain consistent.
Preparation, estimating and tendering
Preparation defines the work to be priced. The contractor estimates labour, materials, plant, subcontract work, overheads and risk against each item. Tendering is the wider process of issuing the documents, answering queries, receiving bids and evaluating them. Unclear descriptions or implausible quantities should be resolved before the price becomes a contractual commitment.
How the BQ is used later
- Work is described and measured from the coordinated design.
- Contractors enter rates and submit their tenders.
- The bids are checked for scope, qualifications and price.
- The agreed BQ supports the construction contract.
- Progress is recorded through construction measurement.
- Changed work is assessed as a variation or on a time-and-materials basis.
Common weaknesses
Typical problems include duplicated work, missing ancillary operations, inconsistent units and compound items that are difficult to measure. References such as “as specified” are risky when the document or revision is not explicit. A strong BQ makes assumptions visible and prevents each tenderer from pricing a different interpretation.
Bills of quantities and Caturix
Caturix supports quotations built from standardised Swiss NPK items and clearly written free-text items. Descriptions, quantities and prices remain structured and can continue into the project once a quotation is accepted. The bill of quantities therefore stays connected to estimating, delivery and reporting instead of becoming an isolated file.
Frequently asked questions
Is preparing a bill of quantities the same as tendering?
No. Preparing the bill defines and quantifies the work. Tendering is the wider procurement process in which documents are issued, questions are managed, bids are received and evaluated, and an appointment is made.
Does a Swiss bill of quantities have to use NPK items?
No. It may combine standardised NPK items with clearly written project-specific items. NPK provides a consistent description structure, but the selected characteristics and project conditions still need to be complete and accurate.
Who prepares the bill of quantities?
Depending on the project, it may be prepared by a quantity surveyor, cost consultant, architect, engineer or specialist planner. The author needs to understand the design, measurement rules, execution conditions and package interfaces.
Sources and editorial review
RICS NRM 2: Detailed measurement for building works – guidance on the purpose, preparation and composition of bills of quantities.
CRB: Guidance on preparing Swiss bills of quantities – official German-language notes on complete and unambiguous work descriptions.