Paint
Walls, coats, Behr door/window sizes. 350 sq ft/gal per coat from PaintCare + SW/BM bands. 10% waste is a convention, not a TDS.
Paint calculatorUS DIY project-cost lab
How much to buy this month — not how pretty the rectangle is.
DIY Project Cost is four free, client-side calculators for US homeowners. Math runs in your browser. The moat is cited manufacturer yields, labelled waste conventions, and a price basket dated 2026-08-27.
Price Index 2026-08-27
Concrete
Slab L×W×depth. 80 lb bag = 0.60 cu ft (Quikrete 1101 / Sakrete). Round up. Optional 10% toggle. Ready-mix $/yd³ stays unofficial.
Concrete calculatorDeck
5/4×6 actual 1.0×5.5 in. 2.182 LF/sq ft. Trex 5% waste. PT board and 2×8 joist prices are zip-localized — you type them.
Deck calculatorDrywall
4×8 = 32 sq ft (USG J371). Subtract doors/windows, not boxes. 10% waste is convention. UltraLight $15.58, alt $16.68 same day.
Drywall calculatorThe price-index promise
Dated, not live
Every SKU is Home Depot online on 2026-08-27, zip not pinned. If we could not verify a national shelf price, the cell is null or a labelled unofficial band.
Yields from PDFs
Bag yields, sheet area, and board width come from manufacturer data sheets. Formulas live in
src/data/with unit tests.Waste, labelled
Manufacturer calculators usually round up with no waste percent. 5/10/15% toggles are conventions (Trex 5%, retailer 10/15) and said so on every tool.
No server, no upload
Your room sizes never leave the phone. Static files nginx can serve on a cheap VPS. Machine-readable basket at /prices.json.