BIM dimensions are a shorthand for what information is added to a model and what it is used for: 3D for geometry, 4D for time, 5D for cost, then 6D and 7D. The first three are used consistently across the industry. The higher numbers are not: sources disagree on what 6D and 7D mean, and no standard, ISO 19650 included, defines any of them.
At a glance
| Dimension | Usually means | Agreed? |
|---|---|---|
| 3D | Geometry: the coordinated model | Yes |
| 4D | Time: elements linked to the programme | Yes |
| 5D | Cost: quantities linked to rates and budgets | Yes |
| 6D | Sustainability (energy, carbon) in some sources; facility management in others | No |
| 7D | Facility management and operation in some sources; sustainability in others | No |
| 8D and beyond | Safety, and other uses, in a few publications | No |
What each one involves
- 3D: the model itself, with elements in the right place and with the right data, federated and coordinated.
- 4D: model elements linked to programme activities, usually by location and work package codes, so the sequence can be played and checked.
- 5D: quantities taken from classified elements, mapped to cost items and priced, so the cost of a design change can be seen quickly.
- 6D and 7D: depending on the source, either analysis for energy and embodied carbon, or the asset information used in operation and maintenance.
How the terms are used on projects
The dimensions are useful in conversation and in marketing: "we do 4D" tells a client that the programme will be linked to the model. They are less useful in contracts and requirements, because "6D" can mean two different things to two parties. Information requirements should instead name the use (for example clash coordination, construction sequencing, cost planning, asset handover), the information needed for it, and when.
Variations
- UK and European sources often use 6D for sustainability and 7D for facility management.
- Some North American and vendor sources reverse them, or use 6D for facility management.
- Some publications add 8D (safety), 9D (lean construction) or 10D (industrialised construction); these are not in general use.
Common misunderstandings
- "7D is a higher level of BIM." The numbers describe uses, not maturity or quality.
- "ISO 19650 defines the dimensions." It doesn't; it speaks of information requirements and uses.
- "Asking for 6D is a clear requirement." Without saying what information, for which purpose, at which milestone, it can't be priced or checked.
Where to read more
The ISO 19650 series and EN 17412-1 (level of information need) for how requirements are actually stated; published lists of BIM uses (for example the Penn State BIM uses) for naming uses precisely; and the lessons on linking the programme (4D) and quantities to an estimate (5D).