Where our numbers come from, how we check them, and what we do when we get one wrong.
A calculator is only worth using if the math behind it is right. This page sets out how we build the tools on ConcreteCalcTools, the published sources we check our figures against, how often we review them, and the policies that keep advertising separate from the results you see.
Volume math is plain geometry: multiply length by width by thickness and divide the result by 27, since a cubic yard is always 27 cubic feet. Bag counts come straight off the yield printed on the bag itself, an 80 pound bag of concrete mix runs about 0.60 cubic feet and a 60 pound bag about 0.45, which is the entire reason 45 or 60 bags fill a yard. Materials sold by weight, gravel and asphalt among them, get converted from that same volume figure using a standard density rather than a number we picked. Each calculator page carries a worked version of its own math, step by step, so you can run it by hand and land on the same result.
Where a number can vary or be argued about, we check it against a primary source and cite it on the page. The ones we lean on most:
When a figure is a genuine range, like the delivered price of ready-mix concrete, we give the range and the year rather than pretending there is one fixed number.
Our tools size a material order. They are not a substitute for a structural engineer, a building inspector or your local code. Real materials behave differently than tidy formulas: damp sand weighs more, crushed stone compacts, a rough subgrade eats concrete, and shingle waste climbs on a cut-up roof. That is why most calculators here build in a waste factor and tell you to round up. For load-bearing work, permits, or any order over a yard or two, confirm the final number with your supplier or a licensed professional before you buy.
A guide or calculator gets a first pass at publication and another look any time a cited figure moves, a code section gets revised, or a reader points out a problem; the date stamped on a page tells you when that last happened. Chris Terry owns ConcreteCalcTools through Encore Promotional Products and signs off on the sourcing across the site. The authors page lists who actually drafts each guide and what gets checked before it ships.
Spot a calculator returning a bad result, or a guide citing a figure you can show is off? Say so through the contact page, no account or form required beyond that. We would rather fix a figure the same week than leave a defensible-sounding error standing.
Display ads and a handful of affiliate links to suppliers and contractor-quote services, Amazon Associates among them, are what keep every tool here free. A purchase through one of those links can earn a commission at no cost to you, but that revenue never touches a formula, a yield, or which product gets recommended in a guide. Every page carries the same ad labeling and affiliate disclosure at the foot.