Last updated: October 24, 2026
A calculator is only useful if you can trust the number it gives you. This page explains how we build, check and update every tool on QtyHome.
1. We start with the question people actually ask
Each calculator answers a specific shopping question, such as “how many 80 lb bags of concrete do I need for a 10 by 10 slab?” We build the tool around the measurements a homeowner can take with a tape measure, in both imperial and metric units.
2. Figures come from published sources
Bag yields, coverage rates and densities come from manufacturer data sheets, product labels and other published references. We cite the source on the page. When sources disagree, we explain the range and use a cautious figure, so you are less likely to come up short.
3. The maths is shown, and tested
- Every calculator shows the formula it used for your result.
- Before a calculator is published, we test it against worked examples that we calculate separately, in both unit systems.
- We check unit conversions in both directions, so switching units does not change your measurements.
- Bag and item counts are always rounded up, because you cannot buy part of a bag.
4. Clear limits
We say what a calculator does not cover. Our results are estimates for planning and shopping, not engineering advice. Where safety or building codes matter, we tell you to check with your local building department or a professional.
5. How we use AI tools
We use AI tools to help with research, drafting and code. They do not decide our numbers. Formulas are tested with worked examples, and figures are checked against the sources we cite before a page goes live.
6. Independence
No brand pays to be included in a calculator or mentioned in a guide. If QtyHome ever uses affiliate links or sponsored content, we will label it clearly on the page where it appears. Advertising, if shown, never changes a result.
7. Updates and corrections
Each page shows when it was last updated. We review calculators when products, standards or sources change. If you find an error, please tell us, with the page and the numbers you used. We fix confirmed errors quickly and update the date on the page.