Introduction
If you are planning a construction project of any size, you will almost certainly come across the term “bill of quantities” at some point. It is one of the most important documents in the construction process, yet it is also one of the least understood by people outside the industry.
In this complete guide, we explain what a bill of quantities is, what it contains, how it is prepared, who needs one and why it is such a valuable tool for controlling costs on any building project. Whether you are a homeowner planning an extension, a builder tendering for work or an architect advising your client, this guide will give you a clear understanding of the BoQ and how it can benefit your project.
For our dedicated service page with pricing information, see our bill of quantities service. For a shorter introduction, see our earlier article on what is a bill of quantities.
What Is a Bill of Quantities?
A bill of quantities (BoQ) is a detailed document prepared by a Quantity Surveyor that lists every individual item of work required to complete a construction project, together with a measured quantity for each item. The items are organised in a logical trade-by-trade sequence, following recognised measurement rules, so that contractors can price each item and produce a total tender sum.
The primary purpose of a BoQ is to provide a common basis for tendering. When all contractors price exactly the same measured quantities and described items, the client can compare tender submissions on a genuinely like-for-like basis. Without a BoQ, contractors interpret the drawings differently, include different items, make different assumptions and produce tenders that are impossible to compare fairly.
Key point: A bill of quantities creates a level playing field for tendering by ensuring every contractor prices exactly the same scope of work, measured to the same rules.
What Does a BoQ Contain?
A typical bill of quantities is divided into several distinct sections, each serving a specific purpose. Understanding these sections will help you read and interpret a BoQ with confidence.
Preliminaries
The preliminaries section covers the general items that are not directly related to a specific trade but are necessary for the project to proceed. These include site set-up and management, temporary facilities (welfare, storage, security), scaffolding, insurance requirements, project management, health and safety provisions and any employer’s requirements. Preliminaries typically account for 8 to 15 per cent of the total contract value on domestic projects and 10 to 20 per cent on larger commercial projects.
Measured Works
The measured works section is the core of the BoQ. It lists every item of physical work required on the project, organised by trade or element. Each item includes a description of the work, a unit of measurement (such as metres, square metres, cubic metres, number or kilograms) and a quantity. The contractor prices each item by entering a rate (unit price) and an extension (rate multiplied by quantity).
Typical trade sections in a domestic BoQ include:
- Substructure – Excavation, concrete foundations, ground floor slab, damp-proofing
- Superstructure – External walls, internal walls, upper floors, roof structure and coverings
- Finishes – Plastering, tiling, floor finishes, painting and decorating
- Mechanical services – Plumbing, heating, ventilation
- Electrical services – Wiring, lighting, power, fire alarm
- External works – Drainage, paving, landscaping, fencing
Provisional Sums
Provisional sums are allowances included in the BoQ for items of work that cannot be fully defined or measured at the time of tender. There are two types: defined provisional sums (where the work is described sufficiently for the contractor to make reasonable allowance in programming and pricing preliminaries) and undefined provisional sums (where the work is not sufficiently defined). Common examples include utility connections, specialist finishes selected after contract award and contingency allowances for unforeseen work.
Prime Cost (PC) Sums
Prime cost sums are allowances for materials or goods that are to be selected by the client or architect after the contract is signed, such as kitchen units, sanitaryware, ironmongery and light fittings. The BoQ includes a monetary allowance for each PC sum, and the actual cost is adjusted at final account stage based on what is actually selected and purchased.
Daywork Schedule
A daywork schedule provides rates for labour, materials and plant that will be used to value any work that cannot be measured and valued using the BoQ rates. Daywork is typically used for small, ad-hoc tasks or variations where it is impractical to measure the work in advance. The schedule establishes the hourly or daily rates that will apply, giving cost certainty even when the scope of daywork is unknown.
How a BoQ Is Prepared
Preparing a bill of quantities is a skilled, methodical process that requires a thorough understanding of construction methods, materials and measurement conventions. Here is an overview of the steps involved.
Step 1: Review the Drawings and Specification
The Quantity Surveyor begins by studying all available project information, including architectural drawings, structural engineer’s drawings, the specification and any relevant reports (ground investigation, party wall, ecology). This stage identifies the full scope of work and any areas where information is missing or ambiguous.
Step 2: Take Off Quantities
“Taking off” is the process of measuring every item of work from the drawings. Today it is most commonly done using on-screen measurement software that allows dimensions to be taken directly from PDF or CAD drawings. Every item is measured according to the rules set out in the New Rules of Measurement (NRM2), which is the RICS standard for detailed measurement in the UK.
Step 3: Write the Descriptions
Each measured item is given a detailed written description that follows the conventions of NRM2. The description must convey enough information for the contractor to understand exactly what is required and to price the item accurately. It includes the type of work, the materials to be used, the size or dimensions, the method of fixing or application and any special requirements.
Step 4: Compile and Format the BoQ
The measured items are compiled into a formatted document, organised by trade section, with columns for item references, descriptions, units, quantities, rates and extensions. A summary page brings together the totals from each section to produce an overall tender total. The finished BoQ is then issued to tenderers along with the drawings and specification.
Who Needs a Bill of Quantities?
A BoQ is valuable on almost any construction project, but it is particularly beneficial in the following situations:
- Competitive tendering – If you are inviting multiple contractors to tender for your project, a BoQ ensures fair, like-for-like comparison
- Cost control during construction – The BoQ provides a detailed baseline against which to measure progress, value interim payments and assess the cost impact of variations
- Complex projects – Projects with multiple trades, complex detailing or significant structural work benefit enormously from the clarity a BoQ provides
- Commercial projects – Most commercial construction contracts are let on the basis of a BoQ prepared to NRM2 standards
- Domestic projects – Homeowners planning extensions, loft conversions or new builds can use a BoQ to obtain genuinely competitive quotes
BoQ vs Estimate vs Schedule of Works
These three documents are frequently confused, but they serve different purposes. The table below summarises the key differences.
| Feature | Bill of Quantities | Estimate | Schedule of Works |
|---|---|---|---|
| Prepared by | Quantity Surveyor | QS / Estimator | QS, architect or client |
| Measured quantities | Yes (detailed) | Yes (summarised) | Not usually |
| Contains prices | Blank for contractor | Yes (QS rates) | May or may not |
| Primary purpose | Tendering & cost control | Budget forecasting | Define scope of work |
| Measurement standard | NRM2 | Varies | None |
| Best for | Competitive tenders | Early budgeting | Small works, maintenance |
For more on the differences between these documents, see our guides on schedules of works and cost plans vs estimates.
Benefits of Using a BoQ
The investment in a professionally prepared bill of quantities delivers a wide range of benefits throughout the project lifecycle:
- Fair tendering – All contractors price the same scope, eliminating guesswork and enabling genuine comparison
- Fewer disputes – A clear, measured description of every item reduces the risk of disagreements about what is included in the contract price
- Accurate valuations – Interim valuations and progress payments can be calculated precisely using the BoQ rates
- Change management – Variations can be valued fairly using the rates established in the BoQ
- Final account clarity – The final account is prepared by adjusting the BoQ for variations, provisional sums and PC sum adjustments
- Better value – Projects tendered with a BoQ typically achieve lower tender prices because contractors do not need to include risk allowances for undefined scope
Tip: Even on small domestic projects, the cost of preparing a BoQ is typically recouped many times over through more competitive tender prices and fewer variations during construction. It is one of the best investments you can make at the pre-construction stage.
How Much Does a BoQ Cost?
The cost of preparing a bill of quantities depends on the size and complexity of the project. As a rough guide:
- Domestic extension or loft conversion: £500 to £1,500
- New build house: £1,000 to £3,000
- Small commercial project: £2,000 to £5,000
- Large commercial project: £5,000 to £15,000+
At First4Estimating, we prepare bills of quantities for projects of all sizes across the UK. Our BoQ service is competitively priced and delivered by qualified Quantity Surveyors working from your drawings and specification. Send us your plans for a fixed-price quotation.
For competitive tendering support, our tender pricing service can help you manage the entire tender process from BoQ preparation through to tender analysis and contractor recommendation.