Our Methodology

Every coverage rate, waste percentage, and yield figure on GetTheAmount is sourced from manufacturer specifications and published industry-standard tables, not a rounded rule of thumb applied uniformly across every material. Where sources genuinely disagree, or a figure varies meaningfully by product or brand, we say so on the relevant calculator page rather than averaging it into one falsely precise number.

Where the numbers come from

Coverage rates for paint, wallpaper, siding, and similar surface materials are drawn from manufacturer label data and published product spec sheets — figures like the standard 350-400 sq ft per gallon range for interior latex paint reflect the range typically printed on the can, not a single invented average.

Waste percentages for tile, flooring, and paver layouts come from established trade practice for each specific pattern — a straight lay, diagonal lay, and herringbone lay genuinely produce different amounts of cutting waste because the cutting geometry at borders and corners is different, not because of an arbitrary safety margin applied more heavily to one pattern than another.

Bulk material yield figures — the real cubic-foot yield of a 60lb, 80lb, or 90lb bag of concrete, or the tons-per-cubic-yard conversion for different stone types — come from published manufacturer yield tables and standard industry conversion figures, which we cross-check against multiple sources when available since bulk material density can vary somewhat by specific product and quarry source.

Reference figures used across the calculators

These are the core reference figures cited across multiple calculators and guides on GetTheAmount, gathered in one place so they're easy to check against the source material yourself:

• Paint coverage: roughly 350-400 sq ft per gallon for interior latex wall paint, one coat on smooth, primed drywall — the range printed on most major-brand paint cans; budget-formula and some eco/low-VOC lines can run lower, closer to 250-300 sq ft/gallon, so always check the specific can.
• Tile waste by layout: roughly 10% for a straight (grid) lay, 15% for diagonal, 20%+ for herringbone and other interlocking patterns — standard trade-practice ranges reflecting how much of each border tile needs an angled versus straight cut.
• Concrete bag yield: approximately 0.45 cubic feet per 60lb bag, 0.6 cubic feet per 80lb bag, and 0.675 cubic feet per 90lb bag of mixed concrete — figures published on standard general-purpose concrete mix bags; specific formulations (fast-set, fiber-reinforced) can vary slightly.
• Cubic yard conversion: 1 cubic yard = 27 cubic feet (a cube 3ft x 3ft x 3ft) — a fixed geometric conversion, not a sourced figure, applied identically across every bulk material calculator (mulch, soil, gravel, concrete).
• Roofing square and pitch multipliers: 1 roofing square = 100 sq ft; pitch multipliers run roughly 1.03-1.05 at low slope (3:12-4:12), 1.12-1.15 at moderate slope (6:12), and 1.41+ at very steep slope (12:12+), derived from the trigonometric relationship between rise, run, and true surface area.
• R-value by climate zone: sourced from U.S. Department of Energy climate zone maps and recommended R-value tables for attics, walls, and floors, which are periodically revised — see the insulation R-value by climate zone guide for the zone-by-zone figures.
• Room AC BTU baseline: roughly 20 BTU per square foot as a starting baseline before ceiling-height, sun-exposure, and occupancy adjustments — a widely used HVAC sizing rule of thumb for room-level (not whole-house) cooling, refined with the adjustment factors covered in the BTU calculator and its guide.

What we don't do

We don't apply one flat waste percentage across every material and layout regardless of whether it's actually justified for that specific case, and we don't round figures to convenient numbers that happen to look cleaner than the sourced figure. Where a material genuinely has a range rather than a single number (like gravel density varying by stone type), the calculator reflects that range rather than picking one number and presenting it as universal.

Structural and safety-critical work

Calculators covering structural or safety-critical work — concrete footings, decks, stairs, roofing, fencing — carry a standing disclaimer that the result is an estimate, not a substitute for checking local building code or consulting a licensed professional. Material-quantity math and structural design are different disciplines, and getting the bag count right doesn't mean a footing depth or a stair rise/run has been verified against your specific local code.

Corrections and updates

Product formulations and published figures change over time. Coverage and yield figures are periodically re-checked against current manufacturer data, and if you find a calculator that looks off for your specific product, the contact page is the fastest way to flag it — corrections get made to the underlying figure a calculator uses, not just the one page where the discrepancy was noticed.