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.
None of the formulas here are proprietary. Concrete volume is length times width times thickness, converted to cubic yards by dividing by 27. A cubic yard is 27 cubic feet, always. Bag counts use the yields manufacturers print on the bag, so an 80 pound bag of concrete mix yields about 0.60 cubic feet and a 60 pound bag yields 0.45, which is why it takes 45 or 60 bags to fill a yard. Aggregate and asphalt are sold by weight, so those tools convert volume to tons using standard densities. We use the same arithmetic a contractor would, and we show the worked example on each page so you can follow it by hand if you want.
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.
Each tool and guide is reviewed when we publish it and again whenever a source figure changes, a reader flags a problem, or relevant code is revised. Pages that carry a date show when they were last updated. Editorial standards across the network are maintained by Chris Terry, who owns and operates the site through Encore Promotional Products.
If a calculator returns a wrong result or a guide states a number you can show is off, email us and we will check it against the source and fix it. We would rather correct a figure quickly than defend a bad one. There is no form to fill out and no account to create. The fastest way to reach us is the contact page.
ConcreteCalcTools is free to use and pays for itself through display advertising and a small number of affiliate links to suppliers and contractor quote services. If you click an affiliate link and make a purchase, we may earn a commission at no additional cost to you. Advertising and affiliate revenue never influence the formulas, the yields or the recommendations in our tools and guides. Ads are labeled, and the affiliate disclosure appears at the foot of every page. As an Amazon Associate we earn from qualifying purchases.