How we verify our calculators

Where the figures come from

This is a different kind of source problem than a personal-finance site, which can lean on a single government agency for almost every figure. There's no equivalent single authority for "how much waste should a tile layout have" or "how many square feet does a gallon of paint cover" - so figures here come from a tier of sources, used in this order of preference:

• Building codes and government guidance - the International Residential Code (IRC/IECC) and similar, and public guidance from bodies like the DOE, for anything code-adjacent (insulation R-values, minimum slab thickness, and similar).
• Industry standards and trade-association technical bulletins - ASTM standards, and publications like NRMCA's Concrete in Practice series, the TCNA Handbook for tile, and similar bodies specific to a trade.
• Manufacturer spec sheets - used only for product-specific constants that don't have an industry-wide standard figure, such as a specific concrete mix's bag yield or a specific paint line's coverage rate. These are labeled "per [manufacturer]" on the page, and every input using one is editable, since a different product will differ.

Never used as sources: other calculator sites, blogs, forums, or AI-generated content, regardless of how often a figure appears across them.

Right now, 43 of 162 calculators carry a "Sources" section with 56 links, including quikrete.com, nrmca.org, codes.iccsafe.org, nfpa.org, astm.org, aacounty.org. The remaining calculators are pure geometry (area, volume, unit conversion) where the formula itself is the source and is written out in the "How to Calculate" section.

How each calculator is tested

The checks depend on what the calculator does, but they follow the same pattern:

• Competitive check first. Before a calculator is built, we compare it with existing tools covering the same question, so the calculator adds something genuinely missing or done poorly elsewhere rather than duplicating what's already available.
• Worked example. Each page prints a step-by-step example. The numbers in it are computed from the same logic that drives the calculator, so the example and the default result agree.
• Independent reference implementation. Where a calculator's math is more than simple geometry, a second implementation is written separately and compared against the calculator on thousands of random inputs, including boundary values, before it ships.

These checks catch arithmetic, geometry, and transcription errors. They cannot tell whether a real jobsite's conditions match the calculator's assumptions, which is why every page links to its sources and states its assumptions plainly.

When the numbers are updated

Figures that change - a code cycle update, a revised manufacturer spec sheet - are updated when the source publishes a change. The "Last reviewed" date on each calculator shows the last site-wide review, currently September 2026.

What is not modelled

Each calculator answers one material-quantity question and says on its page what it leaves out. No calculator on this site performs structural engineering, sizes load-bearing elements, or checks building-code compliance for your specific jurisdiction. Results are estimates for planning and shopping-list purposes, not professional, engineering, or legal advice. The Disclaimer has the full list of limitations.

Reporting an error

If a result looks wrong, use the "Report an error" link under the title of any calculator, or email [email protected]. The most useful report names the page, the numbers you entered, the result you expected, and the source you're comparing against. Confirmed errors are corrected against the cited source.

Independence

rightquantity.com currently has no ads and no affiliate links, needs no account, and runs its calculations in your browser without sending what you type anywhere. Results are never shaped by a product we're paid to recommend. If that changes, this page and the Privacy Policy will be updated first.