The estimate matures with the design

The less design you have in hand, the coarser your method must be — and the wider your honest accuracy range. An estimate's class reflects how much of the project is actually drawn and specified.

Conceptual / order-of-magnitudeAlmost no drawings. Priced by $/SF or $/key. Used for feasibility and go/no-go.

SchematicMajor systems defined. Priced by assembly and parametric models. Funds a project budget.

Design developmentQuantities firming up. Line-item pricing starts to replace parametric factors.

Hard bid / definitiveFull documents. Detailed takeoff and priced unit costs — the bid you sign.

Estimate classes & expected accuracy

A common industry framework (AACE International). Ranges tighten as design maturity increases. Calibrate the percentages to your own historical bid-vs-actual data.

Class	Design maturity	Typical use	Accuracy range
Class 5	0–2%	Order-of-magnitude	−30% / +50%
Class 4	1–15%	Study / feasibility	−20% / +30%
Class 3	10–40%	Budget authorization	−15% / +20%
Class 2	30–70%	Control / bid	−10% / +15%
Class 1	50–100%	Check / definitive	−5% / +10%

Two tools for early-phase pricing

When you lack quantities, you scale from projects you already know.

Cost index — escalate a past cost to today: C_now = C_then × (I_now / I_then) using a published index (ENR, RSMeans city index).
Cost-capacity factor — scale cost by size: C_b = C_a × (Q_b / Q_a)^n, where n ≈ 0.6–0.7 captures economies of scale.

Try both in the calculator below, then read the discipline of pricing the unknowns explicitly — contingency, escalation, and allowances belong on the sheet, not buried in unit rates.