How Many Bags of Concrete Do I Need?
Not sure how many bags to buy? Enter your slab or footing dimensions and pick your bag size. This calculator tells you exactly how many bags to load in your truck.
Choosing the Right Bag Size
Bag size is a tradeoff between cost and convenience. An 80-lb bag yields more concrete per bag, so you'll buy fewer bags and make fewer trips. But lifting and dumping 80 pounds into a mixer wears you out fast.
If you're working alone or have back issues, 60-lb bags are worth the extra cost. They're easier to carry, stack, and pour. You'll go through more bags, but each one is manageable without help.
Stores also stock 40-lb and 50-lb bags, often labeled as fast-setting or high-strength mixes. These work well for post holes and small repairs. Compare the yield per bag on the label to ensure you're getting good value.
Estimating for Waste and Errors
Always buy 10% more than the calculator estimates. Concrete doesn't perfectly fill forms due to voids, spillage, and irregular subgrades. A few extra bags prevent the frustration of running short on the last corner.
Unopened bags store well in a dry location. Stack them on pallets off the ground and cover them with plastic. Bags exposed to humidity harden into useless blocks in weeks, so protect your investment.
For large projects, buy bags in bulk. Many suppliers discount full-pallet orders, and you can return unopened bags within 30 to 90 days if you over-order. Check the return policy before buying.
When Bags Beat Ready-Mix
Bagged concrete makes sense for projects under 1 cubic yard or when access is tight. If a concrete truck can't reach your site, bags might be your only option. You can haul them in a truck or even a wheelbarrow.
Timing matters too. With bags, you mix as you go and stop when you're tired. A ready-mix truck dumps the whole load at once, forcing you to place it all in about an hour. Bags give you control over the pace.
Ready-mix becomes cost-effective above 1 to 1.5 cubic yards. A yard of ready-mix costs $100 to $150 delivered. The same volume in 80-lb bags costs $180 to $225 plus your labor to mix. Do the math before choosing.
Frequently Asked Questions
How much does one bag of concrete cover?
An 80-lb bag yields about 0.6 cubic feet. A 60-lb bag yields about 0.45 cubic feet. Coverage depends on the thickness of the slab.
Should I buy 60-lb or 80-lb bags?
80-lb bags are more economical per cubic foot but harder to lift and mix. 60-lb bags cost more per yard but are easier to handle, especially when working alone.
How many 80-lb bags are in a cubic yard?
One cubic yard is 27 cubic feet, requiring about 45 bags of 80-lb concrete. Always buy a few extra bags for waste and spillage.
Can I mix different bag sizes on one project?
Yes, as long as the concrete type is the same. All bags on a project should be the same mix design to ensure uniform strength and color.
What if I need a partial bag?
Always round up. An open bag of concrete absorbs moisture and hardens quickly. It's better to have an extra bag than to run short mid-pour.