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CalcRafter

How We Calculate and Price

Where every CalcRafter number comes from: the calculator formulas, the federal data behind the price indexes, and the guides behind installed costs.

Calculator math

Every calculator shows its formula in its "How it works" section, so you can check the arithmetic by hand. The math runs in your browser as you type. Nothing you enter is sent anywhere.

Assumptions are stated where they matter: bag yields for concrete, densities for gravel and topsoil, average door and window areas for siding and paint, and waste allowances by job type. Where a supplier's own figure would differ, such as bundles per square on a particular shingle line, the calculator lets you change the input.

Before each release, an automated browser test enters known dimensions into the calculators and compares every displayed result against an independent calculation.

Material prices tracked monthly

Two prices start from a published national average and are carried forward each month with a US Bureau of Labor Statistics Producer Price Index (PPI). The update runs on the 3rd of each month, after BLS publishes the prior month.

  • Ready-mix concrete: NRMCA's 2024 national average of $179.89 per cubic yard (NRMCA), scaled by the BLS ready-mix concrete PPI (BLS PCU327320327320, FRED). Current figure: $185.30 per cubic yard, updated October 3, 2026.
  • Crushed stone: the USGS 2024 national average of $15.88 per ton from the USGS Mineral Commodity Summaries, scaled by the BLS sand, gravel and crushed stone PPI (BLS WPU1321). Current figure: $18.13 per ton, updated October 3, 2026.

The figure is always the anchor times the ratio of the latest index to the anchor year's average index. It is not compounded month to month, so it cannot drift away from the published anchor. If a monthly update would move a price by more than 10%, the update is held back for a manual check. Months before the anchor year are worked backward from the same index, so they are estimates, and the price pages say so.

The Concrete Price Index shows the full history.

Index-only pages

No free primary source publishes a national dollar price for lumber, asphalt shingles or insulation, so those pages show the BLS index itself rather than a made-up dollar figure:

Installed-cost ranges

Installed costs include labor, which varies too much by region for any federal series to capture. For these, CalcRafter uses ranges that overlap across several published 2026 cost guides. Each page says so and links the guides it used:

  • Siding Cost Calculator: Fixr: siding replacement cost; Inch Calculator: siding cost guide; This Old House: vinyl siding cost. Last checked October 4, 2026.
  • Fence Cost Calculator: Fixr: fence installation cost; Inch Calculator: fence installation cost; Bob Vila: fence installation cost. Last checked October 4, 2026.
  • Roof Replacement Cost Calculator: Fixr: roof replacement cost; Inch Calculator: roof replacement cost. Last checked October 4, 2026.
  • Concrete Slab Cost Calculator: $6 to $12 per square foot from published slab installation guides.

These are ranges, not quotes. A local contractor's bid is the number to budget against, and the calculators are there to check whether a bid is in a sensible range.

Corrections

If a number looks wrong, the formula on the page is the first place to check. Errors that are found get fixed in the next release, and price pages carry the date they were last updated.