| Project definition | 0% to 2% of full definition |
|---|---|
| Typical end usage | Concept screening: initial viability, comparing schemes, long-range capital planning |
| Estimating method (general, RP 18R-97) | Capacity factored, parametric models, judgement or analogy |
| Estimating method (road and rail, RP 98R-18) | Gross unit rates such as cost per kilometre, factoring and other parametric models |
| Expected accuracy (80% confidence) | Low: −20% to −50% High: +30% to +100% |
| Other names | Order of magnitude, rough order of magnitude (ROM), screening, strategic, indicative, ballpark, FEL 1 |
| Typical stage | FEL 1; Queensland PCEM: Strategic Planning |
AACE Estimate Classification: Concept Screening
AACE Class 5 Estimate
The first number anyone puts on a project. A Class 5 estimate is prepared from almost no design, often in hours rather than weeks, to answer one question: is this idea worth spending money to study?
Updated 2 October 2026
At a Glance
Class 5 Estimate Characteristics
The five attributes AACE uses to describe each class. Project definition maturity is the one that decides the class; the others follow from it.
Overview
What a Class 5 Estimate Is
A Class 5 estimate sits at the very start of project development, when the definition behind it is somewhere between nothing and 2% of what the finished design will contain. For a road or rail project that usually means a corridor drawn on a large-scale map, an assumed traffic or load requirement, and a handful of route options. There is no alignment, no geotechnical data and no structure design.
Because so little is known, AACE expects the actual cost to land anywhere from 20% to 50% below the estimate on the low side and 30% to 100% above it on the high side, even after a sensible contingency is included. That is not a failure of the estimator. It is an honest statement of how much is still undecided.
Some agencies choose not to formally classify estimates this early at all. When they are classified, the point is to stop a screening number from being remembered later as a budget.
What needs to be defined
Typical status of key deliverables for a road or rail project at Class 5. The class follows the weakest deliverable that materially affects cost, not the average.
- The service need: traffic volumes, freight task or capacity the project must deliver
- A general concept and technology (for example duplication versus a new alignment)
- Route or corridor alternatives agreed by the business or planning stakeholders
- Location, which drives regional cost factors and remoteness
How it is prepared
Class 5 estimates are top-down. On road and rail work the usual tool is a gross unit rate, typically cost per kilometre or per lane-kilometre, taken from comparable completed projects and adjusted for terrain, location and the obvious big-ticket items such as major bridges or tunnels. In other industries the equivalent is capacity factoring or a parametric cost model.
Effort is deliberately low. The value of a Class 5 estimate comes from the quality of the reference data and the judgement applied to it, not from line-item detail that the design cannot yet support.
Worked Example
What the Class 5 Range Means in Dollars
Illustrative figures for a 12 km regional highway upgrade, priced at a cost per lane-kilometre from past jobs: an estimate of $60M including contingency.
| Project risk profile | Accuracy range | 80% confidence range of final cost |
|---|---|---|
| Well understood, low risk (tight end of the band) | −20% / +30% | $48M to $78M |
| Complex or high risk (wide end of the band) | −50% / +100% | $30M to $120M |
Try it with your own estimate
The accuracy range calculator applies the published bands for every class to your figure, and shows where your project might sit within them.
Open the calculatorAACE stresses that these bands are typical outcomes, not targets. The range for a particular estimate should come from a quantitative risk analysis. See P50 and P90 explained.
Avoid These
Common Class 5 Mistakes
- Quoting the point estimate without its range, so a screening figure becomes the expected budget
- Using a single cost-per-kilometre rate across very different terrain, soils or traffic conditions
- Leaving out owner's costs, land, utility relocations and escalation because they are not yet scoped
- Applying a token contingency (10% is common) to an estimate whose uncertainty is several times larger
In Queensland, a Class 5 estimate broadly corresponds to the PCEM Strategic Planning phase. The mapping is approximate; see AACE vs PCEM for how the two frameworks line up.
FAQ
Frequently Asked Questions
What is an AACE Class 5 estimate?
A Class 5 estimate is the least defined estimate in the AACE International classification system. It is prepared with 0% to 2% of project definition, usually for concept screening, using parametric methods such as cost per kilometre or capacity factoring. Its typical accuracy range is -20% to -50% on the low side and +30% to +100% on the high side at 80% confidence.
Is a Class 5 estimate the same as a rough order of magnitude (ROM) estimate?
In practice, yes. Rough order of magnitude, ballpark, screening and indicative are all common names for a Class 5 estimate. The AACE class is more useful because it ties the label to a defined level of project maturity and an expected accuracy range.
Can a Class 5 estimate be used as a project budget?
It should not be. A Class 5 estimate supports decisions about whether to study an idea further. Funding a project against it risks a large overrun because the actual cost could reasonably be double the estimate.
Need AACE-Classified Cost Estimates?
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