Quantity Surveying & Approximate Cost Guide Module 2: The Art of Reading Drawings and the Golden Rules of Quantity Surveying
Dec 1, 2025
In the first module, we learned what quantity surveying, cost estimation, procurement rules, and contract types mean, and why they matter in the bigger picture of a construction project. We also established a solid understanding of terminology and legal context. Now, it’s time to go deeper into how quantity surveying is actually done — because before measuring and calculating, you must first read and interpret the project correctly. If you misunderstand the project drawings, even the most advanced software (including approx.one!) cannot give you accurate results.
Technical Drawings and Project Reading
A construction project is a coordinated set of drawings produced by different disciplines. A quantity surveyor must be able to read and interpret each of these drawings accurately.
Sheets, Scale, and Legends
Every drawing should first be reviewed for three critical elements:
- Sheet Information — Identifies the drawing type, revision status, and scale.
- Scale — Defines the relationship between the drawing and real dimensions. Detailed drawings use larger scales to represent finer construction details.
- Legends and Symbols — Explain the symbols, materials, and components used in the drawings.
Understanding Project Disciplines
Quantity surveying relies on multiple drawing sets, each contributing different measurement data:
- Architectural Drawings — Provide layouts, room functions, and finish information. Used to measure areas, counts, and surface finishes.
- Structural Drawings — Define the load-bearing system, including foundations, columns, beams, and slabs. Used for volume and formwork calculations.
- Mechanical Drawings — Describe plumbing, heating, ventilation, and fire systems. Used to measure pipe lengths, duct runs, and equipment quantities.
- Electrical Drawings — Show lighting, power, and low-voltage systems. Used to calculate cable lengths, conduits, and fixture counts.
Cross-checking between these drawings is essential to avoid inconsistencies and missing quantities.
Quantity Surveying Procedures and Standards
Quantity surveying follows defined procedures and measurement standards. These standards ensure that quantities are calculated consistently and can be verified by all project stakeholders.
The Golden Rules of Quantity Surveying
One of the most common sources of error in quantity calculations is improper handling of deductions.
Exclusions and Deductions
When calculating areas or volumes, elements such as doors, windows, and voids must often be deducted from the total quantity. Measurement standards define when and how these deductions should be applied to ensure accuracy without unnecessary complexity.
Recording Quantities and Worksheets
Quantities are typically recorded using structured worksheets or digital measurement tables. These records ensure transparency, traceability, and ease of review.
Common worksheet types include:
- Excavation and backfill calculations
- Concrete volume calculations
- Formwork surface area calculations
- Reinforcement quantity breakdowns
Modern digital platforms can automate many of these calculations, reducing manual errors and improving efficiency.
Technical Records in Construction Projects
Two important types of technical records are commonly used during construction:
- Variation Records — Document changes or additional work beyond the original contract scope.
- As-Built Drawings — Reflect the actual construction carried out on site, including approved deviations from the original design.
Conclusion
Accurate quantity surveying begins with correctly reading and understanding project drawings. Mastering drawing interpretation and applying consistent measurement rules are essential skills for reliable cost estimation and project control.
In the next module, we will move from interpretation to execution by focusing on practical measurement techniques and workflows.