What our trust signals mean
- Formula shown
- The calculator or its supporting guide explains the calculation method instead of presenting an unexplained answer.
- Assumptions editable
- Inputs that materially affect the estimate are visible or available in customization controls. Defaults are starting points, not hidden facts.
- Sources identified
- Relevant standards, public agencies, manufacturers or other primary references are named and linked where they support a method or default.
- Known limitations disclosed
- Each calculator explains what it does not determine and when project-specific data or qualified review is needed.
- Tested against known cases
- Every live calculator has an automated engine test file. A passing test protects known formulas and conversions; it does not certify every possible real-world project.
Calculator development standard
- Define the task. We separate the user’s measurement or estimating question from decisions the calculator cannot safely make.
- Choose and document the method. Formulas, units and conversions are written explicitly. Where an industry value varies, the value is editable or clearly labeled as an example.
- Separate calculation from presentation. The engine contains the math; model, view and application files handle state, display and interaction.
- Test known cases. Automated tests check core formulas, conversions and important modes before a calculator is published.
- Publish sources and limitations. Supporting text identifies references and tells users what requires field measurements, supplier data, project documents or professional judgment.
Source standard
We prefer sources closest to the underlying fact: government and standards bodies for units or rules, manufacturer technical documents for product-specific yield and dimensions, and clearly dated public data for market ranges. Sources are not endorsements. A source supports only the statement for which it is cited; it does not validate every output from a calculator.
When no universal value exists, the calculator should request project data or expose the assumption. We do not present an illustrative default as a verified local price, code requirement or product specification.
Limitations standard
Every calculator must state its scope and material exclusions. A planning estimate is not a site inspection, construction document, code determination, engineering design, contractor quote or product approval. Users should verify measurements, current local requirements, supplier data and project-specific conditions before purchasing or building.
Review dates and corrections
A “Last reviewed” date records the most recent documented review of that calculator’s method and supporting information. Dates come from source metadata and are not changed automatically during a build. A recent date does not guarantee that every external source or local requirement is unchanged.
If you find a formula, source, wording or accessibility problem, use the page-specific report links or report a problem. Reports should identify the page and explain the expected result; do not include sensitive personal or project information.
Methodology version 1.0.0 · Last reviewed September 11, 2026