Methodology

Geometry

Area, pitch, volume, paint coverage, and bag/yard conversions use standard published relationships: pitch factor √(1 + (rise/run)²), cubic yards = cubic feet / 27, roofing squares = square feet / 100, and manufacturer-style package yields you can edit when the bag in your hand disagrees.

Each calculator page shows the formula in plain language and in compact math. Fixture tests in the repository lock known inputs to known outputs so a future tool cannot silently change a 10×10×4 inch slab.

Cost ranges

We do not operate a bid database. Default dollars are rounded national planning bands with a last-reviewed date, compiled from publicly discussed contractor and retailer ranges—not licensed RSMeans data, not a promise of your city’s labor rate.

Every cost tool emits a range from low and high unit prices you can change. A single dollar figure would be a fake quote. Complexity multipliers (steep roofs, layout-changing remodels) are labeled as coarse bumps, not engineering.

What we refuse to calculate

HVAC pages are not Manual J. Solar pages do not invent tax credits from a ZIP code. Insulation pages do not invent a utility-bill percent. If a result needs a site visit, a load calc, or a tax advisor, the disclaimer says so next to the numbers.

See also the editorial policy and disclaimer.