Estimate Classes — Conceptual, Preliminary, and Definitive
An estimate’s accuracy is bounded by the design behind it. Knowing which class you are producing keeps expectations — and contingencies — honest.
The classes
| Class | Design maturity | Method | Accuracy |
|---|---|---|---|
| 5 — Order of magnitude | 0–2% | Cost/m², capacity factors, analogy | −30% to +50% |
| 4 — Conceptual | 1–15% | Elemental cost per functional unit | −20% to +30% |
| 3 — Preliminary / budget | 10–40% | Elemental + major measured items | −15% to +20% |
| 2 — Detailed / control | 30–75% | Semi-detailed BOQ, priced | −10% to +15% |
| 1 — Definitive / bid | 65–100% | Full BOQ from drawings and specs | −5% to +10% |
Matching contingency to class
- Class 5–4: 20–30% design/estimating contingency on top of the base estimate.
- Class 3: 10–15%.
- Class 2: 5–10%.
- Class 1: 3–5% for residual risk and minor scope gaps.
Contingency covers the known unknowns for that maturity — not scope changes, and not a hidden profit buffer.
Using the right one
A feasibility study needs a Class 4, fast and cheap. A tender needs a Class 1, slow and rigorous. Presenting a Class 4 number with Class 1 confidence is how projects get approved on a budget they cannot be built for.
EngEst Pro supports the full range — the Conceptual Estimate for early Class 4/5 budgeting by building type and area, and the Cost Estimator for a full Class 1 BOQ from measured quantities.
Put this on autopilot with EngEst Pro
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