AACE Estimate Classes
AACE estimate classes rank capital cost estimates from Class 5 (concept screening) through Class 4 (feasibility) to Class 1 (check estimate), each with a typical accuracy range.
In plain terms
Every cost estimate is a range, and its width depends on how much of the project has been defined. AACE International's Recommended Practice 18R-97 sorts process-industry estimates into five classes. Class 5 is the least defined; Class 1 the most.
The ranges are not fixed percentages. They are typical bounds, and the actual range of any estimate depends on technology maturity, site complexity and estimating effort.
Typical range
| Class | Project definition | Typical use | Low range | High range |
|---|---|---|---|---|
| 5 | 0–2 % | Concept screening | −20 % to −50 % | +30 % to +100 % |
| 4 | 1–15 % | Feasibility study | −15 % to −30 % | +20 % to +50 % |
| 3 | 10–40 % | Budget authorisation | −10 % to −20 % | +10 % to +30 % |
| 2 | 30–75 % | Control or bid | −5 % to −15 % | +5 % to +20 % |
| 1 | 65–100 % | Check estimate | −3 % to −10 % | +3 % to +15 % |
A first-of-a-kind green hydrogen plant tends toward the wider end of each range, because electrolyzer and balance-of-plant costs are still moving.
Why it moves LCOH
An LCOH inherits the uncertainty of its CAPEX estimate. In a Class 4 feasibility study, the CAPEX share of LCOH carries a range that may run up to +50 %, so two sites that differ by less than the resulting LCOH range are not clearly ranked yet. Investment decisions typically require at least a Class 3 estimate.
Common mistake
Typical range
−50 % / +100 % (Class 5) to −3 % / +3 % (Class 1, best case) accuracy range around the point estimate[1]