Class 4 estimates are generally prepared based on limited
information and subsequently have fairly wide accuracy
ranges. They are typically used for project screening,
determination of feasibility, concept evaluation, and
preliminary budget approval. Typically, engineering is from 1%
to 15% complete, and would comprise at a minimum the
following: plant capacity, block schematics, indicated layout,
process flow diagrams (PFDs) for main process systems, and
preliminary engineered process and utility equipment lists.
Maturity Level of Project Definition Deliverables
Key deliverable and target status: Process flow diagrams
(PFDs) issued for design. 1% to 15% of full project definition.
Class 4 estimates are prepared for a number of purposes, such
as but not limited to, detailed strategic planning, business
development, project screening at more developed stages,
alternative scheme analysis, confirmation of economic and/or
technical feasibility, and preliminary budget approval or
approval to proceed to next stage.
Class 4 estimates generally use stochastic estimating methods
such as equipment factors, Lang factors, Hand factors, Chilton
factors, Peters-Timmerhaus factors, Guthrie factors, the Miller
method, gross unit costs/ratios, and other parametric and
Expected Accuracy Range
Typical accuracy ranges for Class 4 estimates are
-15% to -30% on the low side, and +20% to +50% on the high
side, depending on the technological complexity of the
project, appropriate reference information, and other risks
(after inclusion of an appropriate contingency determination).
Ranges could exceed those shown if there are unusual risks.