Affiliate disclosure

Which links earn a commission?

Only links to Amazon. They appear in product listings on some calculator and guide pages, where a tool or material suits the job the page covers. Each listing has a "Check price on Amazon" button that opens Amazon in a new tab. Every one of these links carries this site's Associates tracking tag and is marked in the page code with rel="sponsored nofollow noopener", the attribute that tells search engines the link is paid.

A short notice repeating the Amazon Associates statement sits above the first product listing on every page that has one, with a link back to this page. Links to anything other than Amazon, such as a code body or a manufacturer, are ordinary references and earn nothing. We have no other affiliate programmes and no sponsored pages.

How are the products chosen?

By fit to the calculation on the page, using the manufacturer's own specifications. A product is included when its stated size, coverage, capacity or intended use matches the job the calculator works out. Its pros and cons are written only from those published specs and the uses the maker states.

Commission rates play no part in the choice, and no brand pays to be included. We do not buy, use or test the products, and we do not score, rank or star them. A product listing tells you what the item is made for, so you can compare it with what you already own.

Why are no prices shown?

Because Amazon prices change often and a stored price would soon be wrong. The site stores no prices anywhere. The current price is the one Amazon shows when you open the link. Where a calculator offers a cost line, you type in the price you were quoted and it is not saved.

Does commission affect the calculators?

No. The calculators work from formulas and sourced constants and give the same result whether or not a page has product links. Purchase units such as bags and boxes are rounded up only because a part bag cannot be bought, and waste defaults come from a named manufacturer or trade body, not from us. The waste allowances by material guide lists whose figure each default is. Both rules are set out on how the calculators work.

Which Amazon store do the links go to?

Amazon.com, the US store. Readers in the UK and Europe can still follow a link to see the product and its specifications, but availability, prices and model names can differ in your local store. Use the product's model number to find it there, and check the published coverage or size against your result; reading a coverage spec sheet shows where to look. Buying in a local store through your own search earns this site nothing.

What does Amazon see when you click?

The tag in the link lets Amazon credit a qualifying purchase to this site. After you click, Amazon may set its own cookies, and your visit is covered by Amazon's privacy notice. Product images on our pages also load from Amazon's servers. Both points are covered in how we handle data.

For more about the site and its funding, read about the project. Questions about this disclosure can go through the contact page once the address is published. The tools themselves are listed in the full calculator directory.