Cost data & sources

Last reviewed: July 2026

Every calculator on InstallCosts multiplies a measured quantity (square feet, cubic yards, linear feet, drilled depth) by a unit rate. The math is open and shown on each tool's own page. The one thing that is not pure math is the rate itself, so this page is about where those rates come from and what they do and don't represent.

Where the default rates come from

Default rates are US national averages compiled from major published cost guides:

• Angi
• HomeGuide
• HomeAdvisor
• Homewyse

These publish nationwide ranges for the same projects this site covers, and they are the same sources cited in the cost-breakdown section of each calculator. Where the guides disagree, the default sits in the middle of the published range. The headline figure shown at the top of each tool reflects that national range; the editable boxes start at a representative point within it.

What "national average" means here

A national average is a starting point, not a quote. Real prices move with region, site access, material costs at the moment, contractor availability, and season. A septic system, a well, or a driveway in one county can cost half what it costs in another. That is exactly why every rate on every tool is editable: drop in a real number from a local quote and the calculator does the rest of the arithmetic.

How the math works

Each calculator's page has a "How the calculator works" section that spells out the formulas, the densities and conversions it uses (for example 145 lb/ft³ for hot-mix asphalt, 1.4 tons per cubic yard for crushed stone), and any overage or waste factor applied. Nothing is hidden behind the tool, and the same numbers are reproducible by hand.

How often rates are reviewed

Rates are reviewed when the tools are updated, against the sources above. The "last reviewed" date at the top of this page reflects the most recent pass. If a default looks wrong for a specific area, the most useful thing you can do is send a note through the contact page with the tool and what you'd expect.