About ConcreteBag

ConcreteBag is a free set of calculators for figuring out how many bags of concrete you need for a slab, footing, sonotube, or fence post — and roughly what it will cost. Enter your dimensions, and the bag count and price update instantly, right in your browser.

Every calculator uses the same math: convert your dimensions to cubic feet, add a 10% buffer for waste and an uneven subgrade, then divide by the bag's published yield and round up to the next full bag. Reference pages (bags per yard, bags per pallet, and so on) use the same yields without the waste buffer, since those are fixed conversions rather than project estimates.

Figures on this site are estimates for planning purposes only. Actual coverage varies by brand, mix, subgrade, and how carefully concrete is placed and finished. For structural work — footings, foundations, load-bearing posts — check your local building code and talk to a licensed contractor or engineer before you pour.

Affiliate disclosure

Material list links point to Home Depot and Lowe's product search results. ConcreteBag may participate in affiliate programs with these and other retailers; if you click through and make a purchase, we may earn a commission at no extra cost to you. This doesn't affect the bag counts or math shown on the site.

Contact

Questions or corrections? hello@concretebag.com