1. Normalize units
Measurements are converted to SI base units for calculation, then presented in metric and imperial outputs where useful.
2. Use a visible formula
Geometry and conversion logic are implemented as deterministic pure functions. A page explains the same method in plain language.
3. Keep assumptions editable
Waste, paint coverage, package coverage, container size, opening area, and bag yield differ by project and product. Defaults are starting points, not hidden facts.
4. Round only when purchasing requires it
Area and volume retain decimals. Boxes, containers, tiles, and bags round up to whole purchasable units.
5. Test reference cases
Each calculator includes metric and imperial cases, waste behavior, packaging behavior, cost behavior, and invalid-input tests.
6. State the limit
Outputs are planning estimates. Product labels, measurements, local conditions, installers, engineers, and applicable requirements remain authoritative for the real project.