How we calculate

Sources

Each calculator lists its sources at the bottom of the page. We use three kinds:

• Manufacturer data: current technical data sheets for bag yields, coverage rates and product instructions, such as Quikrete's published yields for its concrete mixes.
• Codes and standards: dimensional limits from the International Residential Code (IRC) and industry standards, cited by section. Codes are adopted and amended locally, so your jurisdiction may differ.
• Rules of thumb: where no standard exists, such as a waste allowance, we label the value as a rule of thumb and you can change it.

Checking the numbers

We check every calculator before its page goes live and again whenever it changes. Where a manufacturer publishes reference numbers, such as bag yields or mortar and grout coverage charts, we compare our results with them. We also check the arithmetic, the worked examples on each page and unusual inputs, such as empty or impossible values.

Rounding and waste

• Countable items (bags, tiles, posts, boards) are rounded up to whole units you can buy.
• Where a calculator includes a waste allowance, you see it as a percentage you can change.
• Prices are illustrative defaults, not quotes. Replace them with prices from your local store or supplier. Delivery fees and taxes vary.

Limits

Results are estimates for planning, not engineering or permit documents. They do not replace a site visit, a structural design, the product's own instructions or your local building department. Get professional advice for structural work.