Back to calculator
Construction & DIYGenerated accuracy model review: 2026-05-06
Roofing Materials accuracy and testing
This page documents how Calwarden builds trust for this calculator: source notes, regression-style default tests, limitations, assumptions, unit handling, rounding, and visible change history.
Formula source
- 1. **Pitch Multiplier**: Calculated using Pythagoras ($a^2+b^2=c^2$). A 4:12 pitch has a multiplier of 1.054. 2. **Actual Area** = Footprint × Multiplier × Waste. 3. **Squares** = Area / 100. 4. **Bundles** = Squares × 3.
Test cases
Default input regression check
Generated from the checked-in default inputs and calculate function.
Inputs
- Footprint Area: 1,500 ft²
- Roof Pitch: 4:12 (Low)
- Waste %: 10%
Expected outputs
- Bundles: 53
- Squares: 17.4
- Actual Area: 1,740 ft²
Known limitations
- This page documents the checked-in calculator logic and does not certify results for every real-world edge case.
- Use the result as a planning estimate unless the calculator page states a stricter purpose.
Assumptions
- The footprint area already includes the roof plan area you want to cover, including overhangs if needed.
- Pitch is represented by a preset multiplier rather than a custom measured slope.
- Waste should be zero or greater and the bundle estimate assumes three bundles per square.
Unit handling
- Footprint Area accepts values in ft².
- Roof Pitch accepts one of the configured options.
- Waste % accepts values in %.
- Actual Area is displayed in ft².
Rounding rules
- Number displays use up to 2 decimal places in the calculator UI.
Version history
1.0.0 - 2026-05-06
Generated accuracy and testing page from the current roofing-calculator calculator definition.
Change log
2026-05-06
Published default regression test documentation and metadata fallbacks for Roofing Materials.
Calculator transparency
Accuracy pages are generated from checked-in calculator definitions and can be upgraded with curated review metadata over time.