Methodology — How We Calculate

Every StructMath calculator follows the same discipline: measure → convert → round like a supplier. This page explains where the numbers behind the numbers come from.

Formulas

Each tool page publishes its exact formula under How it works, plus a worked example you can check by hand. The same formulas power automated tests — if a calculator's math drifts, the build fails.

Reference data

• Bag yields (concrete): manufacturer bag labels (80 lb = 0.60 ft³ typical), as printed by Quikrete/Sakrete and equivalents.
• Bulk densities (gravel, stone, sand): published supplier density tables; planning values you should confirm with your yard's ticket.
• Coverage rates (paint): industry can-label spread rates; the calculators let you override with your own product's number.
• Code references (stairs): IRC 2021 residential limits, shown as planning checks — your local amendments govern.

Verification dates

Data pages show a "verified" date (currently October 11, 2026). We re-check reference data and price ranges on a quarterly cadence and whenever a supplier changes published yields.

Prices

Price fields default to typical US retail ranges (dated in the data files) and are always editable — replace them with your store's or supplier's number for a real estimate.

Limitations

Estimates are for planning only — always confirm quantities with your supplier and check local building codes before you buy or build.