What Is a Bill of Quantities? UK Guide

What Is a Bill of Quantities (BOQ) and When Do You Need One?

If you have been involved in a building project of any significance, you have probably heard the term ‘bill of quantities’ – or BOQ. But what exactly is it, why does it matter, and when does your project actually need one?

This guide answers those questions clearly, covering what a bill of quantities contains, how it is used in the construction process, and how to obtain one for your project.

What Is a Bill of Quantities?

A bill of quantities is a detailed document that lists every material, component, and item of labour required to construct a building or carry out a specific scope of works. It is prepared by a quantity surveyor or professional estimator from architectural drawings and a project specification.

Each item in the BOQ is described, measured, and quantified. The contractor pricing the work then applies a rate to each item to produce their tender price. Because every contractor prices the same document, the results are directly comparable – unlike lump-sum quotes, where each contractor may have interpreted the scope differently.

A bill of quantities removes ambiguity from the tendering process. Everyone is pricing the same thing, which means you can compare quotes on a like-for-like basis.

What Does a Bill of Quantities Contain?

A typical BOQ is structured by trade or building element. For a residential project, sections commonly include:

Preliminaries – site set-up, temporary works, project management costs
Substructure – foundations, ground floor slab, drainage
Superstructure – walls, floors, roof structure
Internal finishes – plastering, flooring, ceilings, decorating
Fittings and fixtures – kitchens, bathrooms, joinery
Services – plumbing, heating, electrics, ventilation
External works – landscaping, fencing, driveways

Within each section, individual items are described and quantified – for example: ‘150mm dense concrete block external wall, faced both sides: 45.3m2’. The contractor inserts their rate per square metre and extends the total.

What Is the Difference Between a BOQ and a Building Estimate?

This is a question that often causes confusion. The two documents are related but serve different purposes. A building estimate is prepared by the estimator – it applies rates to quantities to produce a cost figure. It is used internally, to understand what a project should cost.

A bill of quantities is the underlying document of quantities and descriptions. It is given to contractors to price. The contractors fill in their rates; you compare the results.

In practice, the two often go together. ProQuant Estimating produces both the estimate (with our own rates applied) and the underlying BOQ document – so you get both a clear picture of expected costs and a document ready for tendering.

When Do You Need a Bill of Quantities?

Not every project needs a full BOQ. The decision depends on the size and complexity of the works, the number of contractors tendering, and how important it is to compare quotes on a consistent basis.

You Likely Need a BOQ When:

You are tendering to multiple contractors: If three or more contractors are pricing the same job, a BOQ ensures they are all working from identical quantities. Without it, each contractor interprets the scope differently and you cannot meaningfully compare prices.
The project is complex or high-value: For new builds, large extensions, and refurbishments above approximately £100,000, the cost of producing a BOQ is easily justified by the savings it generates in tender management and dispute avoidance.
Contract terms matter: Many standard building contracts (JCT, NEC) reference a BOQ as the basis for valuing variations. If your contract will include a BOQ, you need one prepared properly before work begins.
You need to manage costs during the build: A BOQ allows you to value work done to date, assess the cost of variations, and track the project budget against actual spend.
You are a developer or investor: Accurate BOQs are essential for development appraisals and funding applications. Lenders increasingly require independent cost plans as part of their due diligence.

You May Not Need a Full BOQ When:

The project is straightforward and low-value: A small extension or simple refurbishment can often be managed with a detailed estimate and a single trusted contractor. The cost of producing a BOQ may not be proportionate.
You are using a design-and-build contract: Under D&B arrangements, the contractor takes responsibility for the design and build. A detailed BOQ may not be appropriate, though a cost plan still is.
You are at feasibility stage: Early in the project, you need a budget figure – not a full measured document. A professional estimate based on m2 rates or elemental costs is more appropriate at this stage.

How Is a Bill of Quantities Prepared?

A BOQ is prepared by taking off quantities from architectural drawings – measuring lengths, areas, volumes, and numbers of items against each element of the works. This process is known as ‘taking off’.

Traditionally, taking off was done by hand from paper drawings, using a scale rule and ruled paper. Today, it is typically done digitally using quantity surveying software that allows the estimator to measure directly from PDF or CAD drawings.

The measured quantities are then transferred into a structured document using recognised measurement rules. In the UK, the standard for residential and domestic construction is SMM7 (Standard Method of Measurement, 7th edition) or NRM2 (New Rules of Measurement, 2nd edition), published by the RICS.

How Much Does a Bill of Quantities Cost?

The cost of a BOQ depends on the size and complexity of the project and the level of detail required. For a typical residential extension (two-storey, 50-80m2), a professional BOQ from an estimating service typically costs between £300 and £600. For a new build house or larger development, costs will be higher.

This should be viewed in the context of the project value. On a £200,000 build, a £500 BOQ that enables effective tendering and cost control represents excellent value. The potential saving from a well-managed tender – or a single avoided variation dispute – will typically be many multiples of the cost of the document.

Getting a Bill of Quantities for Your Project

ProQuant Estimating prepares bills of quantities for residential building projects across the UK, including extensions, loft conversions, new builds, refurbishments, and mixed developments. Our BOQs are prepared from your drawings and specification, delivered in a structured format, and available within five working days of receiving all required information.

We also offer a combined estimate and BOQ service – so you receive both an indication of expected costs and a document ready for contractor tendering. Get in touch to discuss your project.