Bill of Quantities

What is a Bill of Quantities?

A bill of quantities is a construction document that quantifies the labor, materials, and expenses required to complete a project. It’s typically compiled during a project’s pre-tender phase, when designs are complete enough for an accurate estimate. Though usually issued alongside tender documents, some construction bids may also include a bill of quantities in the contract.

When is a Bill of Quantities Necessary? 

Regardless of the size or nature of the construction, a bill of quantities is incredibly useful for both tendering and valuation. Larger, more complex projects often require this document to ensure costs remain controlled. 

For owners, the document makes it easy to compare proposals from different contractors. It also clearly defines the scope of work for both parties. This helps the project’s owner structure their budget according to a project’s demand while also ensuring they pay a competitive price.

For contractors, the document levels the field among competitors. It also helps contractors ensure they dedicate the necessary resources to a project and provide accurate pricing.

What’s the Difference Between a Bill of Quantities and a Bill of Materials? 

The two documents differ in purpose, structure, and scope. 

A bill of quantities organizes supplies alongside their associated work rather than breaking them down into individual components. It’s intended to ensure consistent tender pricing and valuation for a project. Each type of antenna in a bill of quantities, for example, appears as a single item with details on measurements, location, quantity, and labor.  

A bill of materials is a granular, hierarchical list of components and supplies. It’s delivered to assist in procurement and production and doesn’t typically include labor or services. An antenna in a bill of materials would be broken down into individual components such as mounts, frame, and screws. 

How is a Bill of Quantities Prepared?

A bill of quantities is usually prepared by an expert cost consultant or quantity surveyor using specialized software. In collaboration with the project’s architect or engineer, the expert defines the full scope of work, then breaks that work down into quantifiable items. These items are generally organized by contractor specialty to facilitate bidding by construction vendors. 

Each item includes all details a contractor needs to accurately estimate costs, including materials, units of measurement, and quantity. Items are further contextualized with drawings and specifications to ensure more accurate cost estimates. Once a contractor’s bid has been finalized, the bill of quantities can also be used for invoicing. 

How is a Bill of Quantities Validated?

A bill of quantities is generally validated by three separate parties. 

The quantity surveyor or cost consultant responsible for compiling and preparing the document performs the initial validation. The project’s architect or engineer then ensures the document accurately reflects the project’s technical scope. Finally, the client checks that the bill is procurement-ready.

Validation involves the following: 

• Verify each item on the bill against its associated drawings and specifications
• Measure and spot check quantities to confirm units of measurement are consistent
• Confirm all items are properly and logically organized
• Check that all descriptions are both clear and specific
• If the bill includes rates or a control estimate, evaluate the number against benchmarks for similar projects
• Ensure the bill can be used for valuation and invoicing outside the tender process
• Submit the document to a third-party expert to review for accuracy and clarity
• Check that there are no redundant or duplicate items

Modern organizations may also leverage autonomous drone technology to create a digital twin of the site, updating it as the project progresses. Instead of having to regularly perform site walkthroughs and submit photos for bidder clarification, owners can provide drone data. As an added benefit, this digital twin can often uncover discrepancies that may not be immediately apparent in paper documentation. The digital twin can also be used to smooth the transition from as-designed, to as-constructed, to as-built, ensuring accuracy every step of the way. While digital twins do not replace quantity surveyors or automatically generate bills of quantities, they provide a verified as-built reference that supports more accurate measurement, validation, and reconciliation.

In addition to grounding the bill of quantities in reality, drone technology can also streamline site audits during a project’s lifespan. As with bidder verification, owners can use routine flights for progress tracking, identifying and addressing potential scope mismatches the moment they become apparent. This directly translates to more accurate cost estimates, lower overhead, and a smoother process from pre-tender to project completion.