How we calculate

Transparency is part of trust. Here's exactly how our estimates are built and checked.

Documented formulas

Every calculator shows the formula it uses and a step-by-step manual method. Nothing is a black box — you can reproduce any result by hand and verify it yourself.

Industry-standard rates

We use widely accepted coverage rates and conversions, for example:

Concrete: 27 cubic feet per cubic yard; 0.45 ft³ per 60 lb bag, 0.6 ft³ per 80 lb bag.
Paint: ~350 sq ft of coverage per gallon per coat.
Roofing: 100 sq ft per square; 3 shingle bundles per square.
Asphalt: ~145 lb/ft³ for compacted hot-mix.

Waste factors

Real projects produce offcuts and spillage, so we build in adjustable waste allowances — typically 5–15% depending on the material and layout. You can change these to match your job.

Expert review

Licensed tradespeople review our formulas and defaults. Meet them on the our experts page.

Updates

We revisit tools as materials and best practices evolve, and we show a "last updated" date on every calculator so you know how current it is.

Estimates, not guarantees

Our results are accurate for planning and budgeting, but site conditions vary. Always confirm final quantities with your supplier or a professional. See our disclaimer.