Construction Cost Calculator
The Quoted Price per Square Foot Is Never the Whole Bill
A contractor's per-square-foot number gives you a base cost, but every real project carries some risk of overruns — a wall that needs extra framing, a permit fee that wasn't in the original estimate. Building that cushion into the number up front, rather than discovering it mid-project, is the difference between an estimate and a budget.
The Formula
The calculator multiplies the project's area by the cost per square foot (or square meter) to get a base cost, then adds a contingency percentage — 10% by default, a common industry-standard allowance for unforeseen costs and overruns — on top of the base cost. Permit and other fixed fees are added last, since they don't scale with area and aren't subject to the contingency markup.
Where This Calculation Matters
- New builds and additions — a per-square-foot cost estimate from a builder is a starting point for a budget conversation, not a final number, and the contingency line makes that explicit.
- Renovation budgeting — older structures tend to carry more unknowns behind walls and under floors, which is a reason to lean toward a higher contingency percentage than new construction.
- Permit-heavy jurisdictions — some municipalities charge substantial plan review and permit fees that have nothing to do with square footage, which is why they're added as a flat amount rather than folded into the per-unit cost.
Worked Example
A 2,000 sq ft addition at $150 per sq ft, with the default 10% contingency and $2,500 in permit fees:
| Step | Calculation | Result |
|---|---|---|
| Base cost | 2,000 × $150 | $300,000.00 |
| Contingency (10%) | $300,000 × 0.10 | $30,000.00 |
| Permit fees | — | $2,500.00 |
| Total estimated cost | $300,000 + $30,000 + $2,500 | $332,500.00 |
How to Use This Calculator
- Select Square Feet or Square Meters.
- Enter the project Area and the Cost per unit area.
- Optionally adjust the Contingency % — defaults to 10%.
- Optionally enter Permit & Other Fees as a flat dollar amount.
- Select Calculate to see the total estimated project cost.
Related Calculations
Working out material quantities first? The Lumber Calculator and Concrete Calculator can help price out individual components before rolling them into this overall budget.