How our estimates are calculated
Estimates only — not a quote. Your final spend depends on your actual site, selections, supplier prices and local requirements.
Your dimensions become quantities
The calculator uses your project dimensions and settings to work out material quantities. Measurements keep their precision; whole purchasable units, such as boards and bags, round up, not down. Bulk materials sold in fractional units can keep fractional quantities.
Waste is an allowance, not a hidden fee
Where a waste allowance applies, it multiplies the material quantity once, before rounding up. Waste cost is shown separately: it is the difference between the estimate with your waste setting and the same calculation at 0% waste. It is already included in the total, not an extra charge to add again. It is not simply the waste percentage multiplied by the whole project cost.
Prices depend on location and source
ZIP-based regional cost indexes adjust baseline material costs for your area where regional pricing is supported. Store prices or U.S. big-box reference prices may also be used, depending on the calculator and available pricing data. A regional index is not a live store quote. Check the price source shown with your result and verify current prices and availability with your supplier.
Money is rounded to cents
Dollar amounts are rounded to two decimal places — cents — at storage or display boundaries. Measurements are not rounded just to make the price look tidy, and intermediate calculations do not repeatedly round money. Line-item totals are summed to a cent-accurate subtotal.
Code and permit information is guidance
Code notes and permit summaries help you know what to ask, but are not a permit determination or engineering approval. Verify requirements with your local building department, including structural details and site-specific conditions, before buying or building.
Which calculator version?
Current calculator version: 2026.10.1. This version comes directly from our calculation-trace module. Saved results can differ from a fresh calculation when calculator math changes; review your inputs and current output before purchasing.