Estimating · 20 June 2026
What's Included in a Full Construction Estimate?
A true estimate prices five things, not just the building. Here is what a real Bill of Quantities covers, and why budgets blow out when it doesn't.
What is a full construction estimate?
A full construction estimate (or Bill of Quantities) is a comprehensive, line-by-line breakdown of every cost required to build a project, from site setup to final handover. Unlike a rough square-metre rate or a "budget guess," a full estimate measures the exact materials, labour, equipment, and allowances needed based on the architectural and structural drawings.
What are the 5 main components of a construction estimate?
When owner-builders or developers price a project, they often only price the building itself. However, a true construction estimate includes five major components:
- Preliminaries: The cost of running the site. This includes temporary fencing, site sheds, scaffolding, crane hire, skip bins, temporary power, and site amenities. Preliminaries often account for 10% to 15% of the total build cost before a single wall is poured.
- Site Works: The cost of preparing the ground. This covers bulk excavation, cut and fill, levelling the pad, retaining walls to hold back soil, and carting spoil offsite. On sloped blocks, site works are frequently underestimated.
- Services: Connecting the site to the street infrastructure. This includes sewer, stormwater, water mains, electrical connections, and NBN, along with the associated authority fees.
- The Building Structure: The core construction costs. This includes the foundation (concrete slab or piers), structural framing, formwork, masonry, roofing, lock-up, and internal fit-out.
- Externals and Landscaping: Everything outside the front door. Driveways, paths, crossovers, boundary fencing, retaining walls, and letterboxes.
Why do construction budgets blow out?
Construction budgets typically blow out because the initial quote relied on Provisional Sums (PS) and Prime Cost (PC) items instead of measured rates. A Provisional Sum is a placeholder allowance for work that hasn't been fully scoped, while a Prime Cost sum is an allowance for an unselected material (like tapware). When the actual work is scoped or the material is chosen, the real cost almost always exceeds the placeholder allowance, coming straight out of the builder's margin.