Quantity surveying insights & guides
Practical guides, tutorials and real-world insights for quantity surveyors and construction professionals.
Estimation vs Quantity Surveying: Key Differences in Construction Projects
Estimation and quantity surveying are closely related construction-cost disciplines, but they have different primary purposes and are most prominent at different stages of a project. Understanding the distinction helps new estimators and quantity surveyors identify how their work supports planning, tendering, execution, payment and cost control.
Project Stages: Pre-Contract and Post-Contract
A construction project can broadly be considered in two stages: the pre-contract phase, where the project is planned and procured, and the post-contract phase, where the selected contractor executes the works.
Pre-Contract Phase
The pre-contract phase occurs before a contractor is appointed to carry out the works. The client or owner develops the project idea and determines what is required, whether this is a house, road, airport or another form of construction work.
Typical pre-contract activities include:
- Feasibility studies and surveys;
- Establishing proposal requirements;
- Design development;
- Measurement and preparation of project quantities;
- Estimating project costs;
- Tender documentation and the tender process.
For example, before constructing a road, initial surveys may be undertaken to determine whether the proposed route and area are suitable. The project team then develops a clearer understanding of how the project can be delivered.
The estimator has a key role at this stage because the project requires a forecast of its expected cost.
Post-Contract Phase
The post-contract phase is the execution phase. It begins after the tender process has resulted in the appointment of a contractor. The contractor is then responsible for carrying out the works in accordance with the contract requirements and the agreed project amount.
At this stage, the focus moves from planning the work to delivering, measuring, monitoring and controlling it. The quantity surveyor has a major role in supporting these processes.
What Is Estimation?
Estimation is the process of determining the expected cost of construction work. To establish a cost, the estimator breaks a work item into the resources and cost components needed to perform it.
This breakdown may include:
- Materials;
- Skilled and unskilled labour;
- Plant, machinery, tools and equipment;
- Supervision;
- Overheads;
- Profit.
The estimator identifies the required quantities of these resources, applies appropriate prices and builds up a rate for the work item. The resulting rate can then be used to calculate the anticipated project cost.
Estimation is particularly important before the project is awarded, because the pricing developed during this period supports tendering and the establishment of project costs. Where new work items arise during execution, a similar estimating process may also be needed to establish the likely cost of that work.
Example: Estimating Reinforced Cement Concrete
Reinforced cement concrete (RCC) is a useful example because it demonstrates how an estimator develops a rate from individual components.
Rather than considering concrete as a single cost, the estimator may consider the resources required to produce and place it, such as:
- Cement;
- Fine aggregates;
- Coarse aggregates;
- Water;
- Admixtures;
- Reinforcement steel, where applicable;
- Labour;
- Concrete pumps, boom trucks and other machinery;
- Tools, overheads and profit.
The estimator determines the quantity and cost of each component and combines them to establish a rate per cubic metre. In the lecture example, a hypothetical rate of 500 USD per cubic metre of concrete is used. This figure is illustrative and the applicable rate depends on the project and pricing basis.
The lecture also refers to a mix ratio of 1:2:4, described as one bag of cement, two bags of fine aggregate and four bags of coarse aggregate. Such resource information is used when determining material requirements for a unit of concrete.
What Is Quantity Surveying?
Quantity surveying is strongly associated with measurement, financial administration, monitoring and cost control during the execution of the project. Once the pre-contract requirements, quantities and pricing basis have been established, the quantity surveyor monitors the work performed against those references.
Key quantity surveying activities described in the lecture include:
- Providing and checking accurate BOQ quantities against drawings;
- Measuring completed work;
- Recording site progress;
- Monitoring quantities against planned quantities;
- Supporting project cost monitoring and control;
- Providing inputs relating to direct project costs;
- Assessing the value of executed work for payment purposes.
Measurement provides the evidence needed to compare planned work with actual progress. For example, if the original scope includes 1,000 cubic metres of concrete and only 500 cubic metres have been completed, then 500 cubic metres remain. This comparison supports progress monitoring.
Cost control also involves comparing actual performance with the original allowance. The lecture gives an example in which a budget was allocated for 100 cubic metres, but the quantity rises to 120 cubic metres. This indicates that the cost is increasing against the original allowance.
Measurement and Valuation of Executed Work
For a measured concrete item, the quantity surveyor may determine the volume of completed concrete using length, breadth and height. The measured quantity is then multiplied by the agreed rate to establish the value of work executed.
Using the lecture's illustrative rate:
| Measured item | Measurement basis | Valuation approach |
|---|---|---|
| Concrete | Volume in cubic metres | Measured quantity × agreed rate per cubic metre |
Where a rate of 500 USD per cubic metre has been agreed, the quantity surveyor does not normally need to rebuild the full material, labour and plant composition every time a completed quantity is measured. The agreed rate is applied to the measured work for valuation purposes.
Drawings, work records and other project documents provide the references needed to demonstrate that the relevant work has been executed and to support payment or recovery of the amount due.
Comparison: Estimator and Quantity Surveyor
| Aspect | Estimation | Quantity Surveying |
|---|---|---|
| Primary focus | Forecasting the cost of work | Measuring, monitoring and controlling the financial effect of work |
| Main project stage | Primarily pre-contract | Primarily post-contract and during execution |
| Typical method | Build up rates from materials, labour, plant, overheads and profit | Measure work completed and compare it with drawings, BOQ quantities and project allowances |
| Concrete example | Determine the cost components required to produce 1 cubic metre of RCC | Measure the completed concrete volume and apply the agreed rate |
| Project purpose | Support pricing, budgeting and tendering | Support valuation, progress monitoring and cost control |
Why a Quantity Surveyor Must Understand Estimation
The distinction is not absolute. A quantity surveyor is not limited to measuring length, breadth and height. Quantity surveyors should understand how estimates and rates are built up because they may need to review material requirements, provide cost information to the project team or assist when an item requires further cost analysis.
For RCC, this means understanding that the measured concrete item is supported by underlying resource requirements such as cement, fine aggregate, coarse aggregate, reinforcement, labour, plant and other costs. This knowledge helps the quantity surveyor interpret rates and support cost-related decisions during project execution.
Key Learning Points
- The pre-contract phase includes feasibility, design, measurement, estimating and tendering activities.
- The post-contract phase is the execution stage after a contractor has been selected.
- Estimators develop expected costs by breaking work into resources and cost components.
- Quantity surveyors measure, record, monitor and control work and costs during execution.
- An agreed unit rate can be applied to measured quantities to value completed work.
- Quantity surveyors need estimating knowledge because measurement, valuation and cost control depend on understanding how construction work is resourced and priced.
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