How Tallyard calculators work

Each calculator's formula is displayed directly on the page, in the “Show the math” section below the result. You see every input, every intermediate step, and the final result. If we apply a waste factor, a rounding rule, or a coverage rate, it appears explicitly in the calculation steps.

For example, the paint calculator uses: gallons = (perimeter × height − doors × 20 − windows × 15) × coats ÷ coverage, where coverage defaults to 350 sq ft/gal (one coat, smooth surface). The formula, the default, and the source of the coverage rate are all visible.

Coverage rates, sizing factors, and code requirements are sourced from four categories, listed in order of preference:

1. Manufacturer product data. Coverage per gallon (paint), yield per bag (concrete), capacity per unit (air conditioning tonnage). These come directly from product data sheets published by manufacturers like Benjamin Moore, Quikrete, Trane, and James Hardie.
2. Building codes. Stair rise and run limits (IRC R311.7), egress window minimums (IRC R310), drain pipe sizing (IPC Table 710.1), insulation R-values by climate zone (IECC Table R402.1.2). We cite the specific code section for every code-derived value.
3. Industry standards. ACCA Manual J for HVAC load calculations, APA for engineered wood, NADRA for deck construction, NKBA for kitchen layout. These fill gaps between manufacturer data and building codes.
4. Aggregated cost data. For cost estimates in guides, we use HomeGuide, Angi, NerdWallet cost reports, and EIA energy pricing. We note the source date and identify that cost data is approximate and regionally variable.

Every calculator page links to its specific sources at the bottom. If a source goes stale (manufacturer updates a product line, code gets revised), we update the calculator and note it in the methodology section.

Calculator results are rounded up to practical purchase units. You can't buy 2.67 gallons of paint, and ordering 5.4 cubic yards of concrete is a recipe for a short pour. So we round the result to the nearest buyable quantity and show both the raw and rounded numbers.

Waste factors are applied before rounding. A 10% waste factor on 4.8 cubic yards of concrete becomes 5.28, rounded to 5.5. The waste factor is always displayed in the formula steps so you can remove it if you're confident in your measurements.

Tallyard calculators produce material estimates for planning. They are not engineering specifications, structural calculations, permit applications, or professional assessments. Several important things they do not account for:

• Site-specific conditions (soil type, grading, drainage, existing structural problems)
• Local code amendments that differ from the model codes we reference
• Material availability and pricing in your specific market
• Labor costs, permit fees, and inspection requirements
• Structural load calculations (always get an engineer for load-bearing work)

For structural, electrical, plumbing, or anything where safety is involved, hire a licensed professional. The calculator gives you a starting estimate for budgeting and material ordering; the professional gives you the final answer.

Buying guides follow a separate process. Each guide is researched by the founder (Ash K.) against current industry data, with total-cost-of-ownership calculations showing their assumptions explicitly. Guide methodology notes (expandable at the top of each article) disclose energy price sources, cost data vintage, and modeling limitations. Sources are linked at the bottom.

Guides do not accept sponsored content, paid placements, or affiliate commissions. Manufacturer names appear only when relevant to the recommendation (naming a specific cold-climate heat pump model, for example). No manufacturer pays for inclusion.