What Does OPCC Mean?
OPCC means Opinion of Probable Construction Cost. It is an estimate of what a project is likely to cost to construct, prepared before bids are received, usually by the design engineer, a cost consultant, or an independent estimator working for the owner. In engineering, OPCC is the standard term for the cost estimate that accompanies a design at each milestone.
Why It's Called an "Opinion"
The word opinion is deliberate. The person preparing the estimate doesn't control labor rates, material prices, contractor workload, bidding competition, or market conditions on bid day. Standard engineering agreements use the term to make clear that the number is a professional judgment of probable cost, not a guarantee that bids will come in at that price.
OPCC vs. Engineer's Estimate vs. Bid
- OPCC: the owner-side estimate of probable cost at a design milestone. Used for budgeting, funding, and design decisions.
- Engineer's estimate: on public work, often the final OPCC prepared at bid time and used to evaluate the bids received. The terms overlap and agencies use them differently.
- Contractor's bid: the price a contractor commits to. It carries the contractor's means and methods, production, overhead, risk, and profit.
The gap between an OPCC and the bids is where owners get surprised. The closer the OPCC is to how a contractor actually prices the work, the smaller that gap.
What Goes Into an OPCC
- Quantities taken from the current design documents.
- Unit costs for labor, equipment, materials, and subcontracts.
- General conditions, mobilization, overhead, and profit markups.
- Contingency sized to the design stage and the known risks.
- Escalation to the expected bid or construction date.
- Written assumptions, inclusions, and exclusions so the number can be defended.
OPCC Accuracy by Design Stage
An OPCC gets tighter as the design develops. Many owners and agencies align OPCCs with the AACE International estimate classification system, which runs from Class 5 (concept screening, least defined) to Class 1 (bid check, most defined). A concept-stage OPCC carries wide accuracy ranges and larger contingency. A construction-documents OPCC should be built from detailed quantities and track closely to the bids.
- Concept / planning: parametric or order-of-magnitude, used for feasibility and funding requests.
- Schematic design: major quantities and systems defined, contingency still significant.
- Design development: most quantities measurable, contingency tied to specific risks.
- Construction documents: detailed quantity-based estimate used to check bids.
Where Sitework OPCCs Go Wrong
On sitework and civil projects, most budget busts come from the dirt: over-excavation the geotech requires, import or export that swings with the balance, rock, groundwater, and haul distances nobody checked. A field-built OPCC prices the earthwork from quantities and production the same way a bidder will, so the owner's number and the bids end up in the same place.
Getting an Independent OPCC
Earthworks NV prepares independent cost estimates and OPCCs for owners, developers, public agencies, and design teams, built from quantities up by field estimators who have priced, bid, and built sitework for their entire careers. Every OPCC includes written assumptions and a risk-based contingency with a rationale instead of a flat percentage.