In Plain English
Quick Answer
A cost estimate calculated using a cost-per-unit formula based on historical data, like dollars per square foot.
Definition
Definition
A parametric estimate uses statistical relationships between project parameters and historical cost data to produce cost projections, typically expressed as a cost per unit such as dollars per square foot or dollars per bed. It provides better accuracy than conceptual estimates but less than detailed quantity takeoffs. Parametric estimating is common in early project phases and for benchmarking.
Context
Why It Matters in Bidding
Parametric estimates let owners and GCs set early budgets and test feasibility before drawings are complete enough for a detailed takeoff. For estimators, they are a fast benchmarking and sanity-check tool against the eventual line-item bid, but they carry real risk if the historical cost-per-unit data is stale or the new project's scope differs from the basis, so they should never substitute for a quantity takeoff at bid time.
Example
Example
During schematic design, an estimator pegs a 120-bed assisted-living project at roughly $310 per square foot using cost-per-bed data from three similar recent jobs, giving the owner a budget order of magnitude months before construction documents exist.
See Also
Related Terms
FAQ
Questions Contractors Ask
When should you use a parametric estimate instead of a detailed takeoff?
Use it in early phases when drawings are too incomplete for quantity takeoff, such as feasibility, programming, or schematic design. It is also useful for benchmarking a detailed bid for reasonableness. Once construction documents exist, a detailed line-item takeoff should replace it for actual bidding and buyout.
How accurate is a parametric estimate?
It is more accurate than a rough conceptual estimate but less accurate than a detailed quantity takeoff, typically carrying a wider contingency range. Accuracy depends entirely on how well the historical cost basis matches the new project's location, scope, quality level, and market conditions, all of which require adjustment factors.
What data do you need for a reliable parametric estimate?
You need historical actual costs from comparable completed projects, normalized for size, location, time, and quality, along with the relevant unit parameter such as square feet, beds, or stalls. Without clean, escalated, and apples-to-apples cost history, the cost-per-unit factor produces a misleading number that can mislead the owner's budget.
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