Methodology

General approach

Each calculator is a small, pure function: given your inputs, it applies a fixed formula and returns a result — no hidden adjustments, no server-side lookups, nothing sent over the network. The same formula that produces the live result on each calculator page also produces the worked example shown lower on that page, so the example can never drift out of sync with the tool itself.

Full derivations for each calculator's formula are shown on that calculator's own page, under "How this is calculated." This page covers the reference values that feed into those formulas and the standard industry assumptions behind them.

Reference values used

• Gravel material density (tons per cubic yard): 1.4 for standard gravel, 1.5 for crushed stone, 1.35 for sand, 1.0 for topsoil. These are commonly cited landscaping supply figures; actual density varies with moisture content and compaction, so a supplier's posted figure for their specific material should take precedence for a large order.
• 10% waste allowance: applied to gravel volume and weight as a separate, clearly labeled line item — standard trade-industry practice to cover compaction, spillage, and uneven sub-grade, not folded silently into the base number.
• Concrete per fence post: 2 bags of 50 lb (approx. 22.7 kg) quick-setting concrete mix per post hole — a common contractor rule of thumb for standard residential fence posts. Taller fences, larger posts, or difficult soil can require more.
• Roof pitch convention: rise expressed per 12 inches of run (the "x/12" system used throughout US residential construction). Angle is derived directly via arctangent; there is no reference constant to vary there.

What these calculators don't do

They don't account for irregular or non-rectangular areas, existing grade or drainage conditions, local building codes or permit requirements, or site-specific factors a contractor would evaluate in person. They also don't cap or reject unusually large or small inputs outright — instead, values well outside a typical residential range trigger an on-page caution so you can double-check your numbers, without blocking a legitimate larger-than-normal project.

For anything structural, permitted, or safety-related, treat these numbers as a starting point for a conversation with a licensed contractor, not a final spec.