Methodology

We publish every formula and assumption. If you spot something wrong, please tell us — we'll fix it and credit you.

Where the numbers come from

• Concrete: ACI 301, Portland Cement Association coverage tables.
• Drywall: USG installation guides.
• Roofing: NRCA waste recommendations, asphalt-shingle manufacturer specs.
• Tile: TCNA Handbook for layout-specific waste percentages.
• Flooring: NWFA installation guidelines.
• Weather: Open-Meteo free API (no key, no tracking).

Every calculator page surfaces the relevant references at the bottom — click through to verify.