Professional guide · Updated 27 October 2026
What is BIM? From a 3D model to information and a bill of quantities
Building Information Modeling (BIM) is a way of managing information about a building or infrastructure asset throughout design, construction and use. The 3D model is part of that process. Its value also depends on the information attached to elements, coordinated versions and traceable sources.
What information belongs to an element?
A window can carry dimensions, level, type, material and a specification reference. Thermal or fire performance is available only when the relevant values have actually been supplied and checked. A modeled object does not prove compliance or data completeness.
Useful information needs context: revision, responsible party, units and meaning. Opening area, glazing area and an ordering dimension can differ. Clear definitions matter as much as the shape on screen.
How do CAD and BIM differ?
| Topic | Typical CAD drawing | Model-based BIM workflow |
|---|---|---|
| Representation | Lines, arcs, blocks and layers | Objects with geometry, properties and relationships |
| Information | Annotations, block attributes and linked documents | Structured properties linked to model objects |
| Changes | Review every affected document | Related views and schedules can update from a shared model; linked files and revisions still require checking |
| Quantities | Measure drawings and interpret the specification | Read geometry and properties, map work items and review scope |
CAD can contain structured information too. BIM concerns the organization, coordination and use of information, rather than a blanket rule that drawings contain no data. An attractive 3D render alone is not a complete BIM process.
BIM is the method; Revit is one of the tools
Revit supports parametric modeling, drawings and schedules. Related views can reflect a change to the same model element. BIM is broader than any one software product: project participants may use different tools and exchange information.
Where does IFC fit?
IFC is an open standard for describing elements, properties and relationships across systems. It supports exchange, but does not guarantee identical interpretation by every application. Check units, placement, classifications, quantities and identifiers after export and import.
How does a BIM model become a BOQ?
- Define scope: buildings, levels, disciplines and design stages.
- Review the model: revision, units, links, missing elements and duplicates.
- Map work items: an element may contribute to several items, and an item may include many elements.
- Apply measurement rules: geometric area is not necessarily payable area; ordering waste is separate from contractual quantity.
- Include unmodeled work: temporary works, protection and site establishment where supported by project documents.
- Keep a review trail: source, unit, calculation rule and location before pricing or approval.
AiN aims to connect model elements, BOQ rows and Excel while retaining professional review and manual completion. Actual behavior depends on the available data and the verified workflow; this guide does not promise automatic recognition of every model or work item.
Quantity source records · BOQ data checks · Infrastructure quantity takeoff
Frequently asked questions
Is every 3D model BIM?
Not necessarily. Inspect its information and relationships, and how the project manages and shares them.
Does BIM replace a quantity surveyor?
No. Applying the specification, contract and measurement rules still requires professional judgment and review.
Does changing a model update every cost?
Only when the relevant mappings and links are maintained. Identify affected items and any manual or outdated data.
Can 2D drawings be used as well?
Yes. Record which quantities came from drawings and which came from models to avoid overlap and preserve traceability.
Professional references
General professional guidance prepared with AI assistance. Check source data, project documents and applicable measurement rules before use.