Types of construction estimates follow the design
An estimate can only be as detailed as the drawings behind it. Early on, it is a screening number from area and building type. At bid time, it is a measured takeoff priced line by line. Each stage uses different methods and carries a different range.
AACE International publishes estimate classification practices: 18R-97 for process industries and 56R-08 for building and general construction. Both sort estimates by maturity of project definition.
Types of construction estimates compared
| Type | Typical design stage | Main method | Typical use |
|---|---|---|---|
| Conceptual / ROM | Program or concept | Square foot, capacity factoring | Go or no-go |
| Budget / schematic | Schematic design | Systems or assemblies | Set the funded budget |
| Design development | Developed design | Assemblies plus partial takeoff | Check against budget |
| Bid / detailed | Construction documents | Full takeoff, unit costs, sub quotes | Price you commit to |
| Change order | During construction | Takeoff of the change | Price added or deleted work |
| Engineer’s / owner’s | Any stage | Varies | Owner’s check on bids |
AACE estimate classes and accuracy
The DOE summary of AACE 18R-97 gives these ranges for process industries, at roughly 80% confidence:
| Class | Project definition | Low range | High range |
|---|---|---|---|
| Class 5 | 0% to 2% | -20% to -50% | +30% to +100% |
| Class 4 | 1% to 15% | -15% to -30% | +20% to +50% |
| Class 3 | 10% to 40% | -10% to -20% | +10% to +30% |
| Class 2 | 30% to 75% | -5% to -15% | +5% to +20% |
| Class 1 | 65% to 100% | -3% to -10% | +3% to +15% |
Building projects use 56R-08, so treat these as a guide to how range narrows, not as building-specific figures.
Conceptual and budget estimates
Conceptual estimates screen feasibility from very little information. Budget estimates set the money an owner will fund, usually from schematic drawings priced by system. Both need a written basis, a range and design contingency. See the conceptual estimate guide and budget estimates.
Estimating methods: square foot, assembly, unit cost and parametric
- Square foot: area times a cost per square foot from comparable projects or a cost database, adjusted for location, quality and date.
- Assembly or systems: each building system priced by its own unit, such as wall area or roof area.
- Unit cost: each measured quantity times a unit cost for labor, material and equipment. The basis of bid estimates.
- Parametric: cost scaled from a known project by a driver such as capacity.
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ROM, preliminary, definitive and engineer’s estimates
Names vary by owner. ROM (rough order of magnitude) is common in government and means conceptual. Preliminary usually means budget-level. Definitive means detailed. An engineer’s estimate is the owner’s own estimate used to judge bids; federal agencies prepare an independent government estimate for construction contracts above the simplified acquisition threshold under FAR 36.203.
Detailed bid estimates and quantity takeoffs
A bid estimate prices complete construction documents: a quantity takeoff of every item, labor at your productivity and rates, material from supplier quotes, leveled sub quotes, general conditions, then markups and bonds. It becomes the price you commit to, so its basis must be traceable line by line.
Change order estimates
Change order estimates price added, deleted or changed work during construction: takeoff of the change, labor, material, equipment, markup as the contract allows, and time impact. See change order pricing.
What every estimate type should state
Whatever the type, write down the basis so the number cannot be misused:
- Documents used, with dates and revisions.
- Estimate type or class and its expected range.
- Cost data sources and dates, and any location or escalation adjustment.
- Inclusions, exclusions and assumptions.
- Contingency, shown as its own line.
An early number without its basis gets treated as a bid. A bid without its basis is hard to defend when scope is disputed.
Trade or whole-project estimates: how to choose
Subcontractors usually need single-trade estimates. General contractors need whole-project estimates, or trade estimates for self-performed work plus leveled sub quotes. Bidmere prepares both at your rates: single-trade estimates from $195 in 48 hours and multi-trade estimates from $1,150.
Frequently asked questions
What are the main types of construction estimates?
Conceptual or order-of-magnitude, budget or schematic, design development, detailed bid estimates and change order estimates, plus the owner’s engineer’s estimate. They differ in how much design exists, the method used and the expected accuracy range, which narrows as the design develops.
What is a Class 5 estimate?
In AACE classification, Class 5 is the least-defined estimate, with about 0% to 2% project definition, used for concept screening. The DOE summary of AACE 18R-97 gives it a range of roughly -20% to -50% on the low side and +30% to +100% on the high side, for process industries.
What is a Class D construction estimate?
Letter classes are used by some owners and agencies, often from Class D (early, conceptual) to Class A (detailed, from construction documents). The meanings vary by organization, so check the owner’s own definitions. AACE’s numbered classes, 5 through 1, are the more widely cited standard.
Which estimate type do I need to bid a job?
A detailed bid estimate: a full takeoff of the construction documents, priced at your rates with leveled sub quotes, general conditions and markups. Conceptual and budget estimates are for decisions before design is complete, not for prices you will be held to.
What is an engineer’s estimate?
The owner’s own estimate of construction cost, used to set budgets and judge whether bids are reasonable. Federal agencies prepare an independent government estimate for construction contracts above the simplified acquisition threshold under FAR 36.203. Public owners often publish it with the bid tabulation.
Can Bidmere prepare any of these estimate types?
Yes. Bidmere prepares conceptual and budget estimates, detailed bid estimates, quantity takeoffs and change order pricing at your rates. You get a fixed price and delivery date within 2 business hours, plan review is free, and you pay only after you accept.