Calculation methodology

Every maintained example is built from units and arithmetic that a reader can reproduce with a basic calculator.

Our calculation order

We keep measurements in explicit units, convert once, calculate the geometric quantity, add any stated planning allowance, convert to the product's purchase unit, and round only at the final purchase step.

Generic assumptions versus product facts

Generic assumptions are labeled as examples. Product yield, coverage, package size and installation instructions should come from the selected manufacturer's current documentation. Structural dimensions and code requirements are not inferred from a cost calculator.

Source hierarchy

Where an external fact matters, we prefer manufacturer documentation, code/standards organizations and established trade organizations. Local price inputs are intentionally editable because a national “average” can be misleading for a specific project.

Corrections

If a formula or cited reference is wrong or outdated, contact us with the page and issue. We correct the maintained guide rather than creating another near-duplicate page.

Verification hierarchy

  1. Project measurements: dimensions measured for the actual job.
  2. Manufacturer documentation: package coverage, yield, installation constraints and product-specific values.
  3. Code/industry references: used for terminology and planning context where relevant.
  4. Calculator arithmetic: transparent conversion and multiplication using the inputs above.

If a manufacturer instruction, approved plan or local requirement conflicts with a generic calculator assumption, the project-specific source wins.

Rounding policy

Intermediate calculations retain precision. Rounding is delayed until the result is converted into a real purchasing unit such as a whole carton, bag, roll or supplier order increment. This avoids compounding small rounding errors across multiple steps.

Update policy

Pages are revised when a formula error is found, a cited source changes materially, or the explanation can be made more checkable. Dates indicate editorial maintenance; they are not intended to imply that universal construction prices stay current.