Reference

How we calculate

Every calculator on Tape & Tally is built to give you an honest, buy-ready number — not a vague estimate. This page explains how the math works and where the assumptions come from, so you can trust the result and adjust it to your own project.

The core method

Most calculators follow the same shape: measure the area or length, add a realistic waste allowance, then divide by the coverage of one real package (a box, bag, gallon or bundle) and round up — because stores sell whole packages, not fractions.

• Area / volume from your measurements (e.g. width × length, or × thickness for concrete).
• Waste you can adjust — sensible defaults per project (8–15%).
• Package sizes based on common US products (box coverage, bag yield, gallon coverage).
• Round up to whole packages, and keep a spare for repairs.

Cost estimates are ranges, never quotes

Cost figures are rough, materials-only guidance with a unit price you can edit. They exclude labor, tools, delivery and tax, and prices vary widely by region and product. Treat them as a starting point — always confirm against real product pricing before you buy.

Accuracy & testing

Each formula is implemented twice — once on the server and once in your browser — and both are checked against the same set of test cases, so the number you see while typing matches the one the page ships with. We use realistic package coverage, but actual products differ: always check the coverage printed on the box or bag, which is the final word.

Privacy

The calculators run entirely in your browser and work with no account. If usage statistics are enabled, they're anonymous — a calculator and a rounded size, never your name, email or IP address. See our privacy policy for details.

Found something off?

We take accuracy seriously. If a result looks wrong or a package size is out of date, tell us and we'll fix it.