How Many Bags of Concrete Do I Need?

It takes 45 bags of 80 lb concrete, 60 bags of 60 lb or 90 bags of 40 lb to make one cubic yard. A 10 x 10 ft slab 4 inches thick is 1.23 cubic yards, which works out to 56 bags of 80 lb concrete or 75 bags of 60 lb, before any extra for waste. For any other job, find the volume in cubic feet and divide by the yield of the bag you plan to buy.

This guide gives bag counts for the jobs people most often pour from bags: small slabs, walkways, post holes and footings. Every figure uses the same bag yields as our Concrete Calculator, so you can check any number here against the tool.

How Much Concrete Is in One Bag?

Premixed concrete is sold by weight but poured by volume. These are the typical yields for standard mixes:

A cubic yard is 27 cubic feet, so 27 ÷ 0.60 = 45 bags of 80 lb. Every row works out to the same 3,600 lb of dry mix per cubic yard: the bag size changes how many trips you make, not how much weight you move. Yields vary a little by brand and product, and fast-setting or high-strength mixes can differ, so check the label on the bag you actually buy.

The Formula

For round holes and tubes, use the cylinder formula instead: cubic feet = 3.1416 × (diameter in inches ÷ 24)² × depth in feet.

Bags of Concrete for Slabs and Walkways

All slabs below are 4 inches thick, the usual thickness for patios, walkways and shed pads. Counts are before waste, exactly as the calculator shows them.

Thickness matters as much as area. A 10 x 10 ft slab at 6 inches is 50 cubic feet, or 84 bags of 80 lb, half as much again as the same slab at 4 inches. If you are unsure which thickness you need, read how thick a concrete slab should be first.

Once a pour passes about 1 cubic yard (45 bags of 80 lb), mixing by hand turns into a long and heavy day. Before you buy 100 or more bags, compare the options in bagged concrete vs ready-mix.

Bags of Concrete for Post Holes

Fence posts, deck posts and mailbox posts are the classic bagged-concrete job. The table shows one hole, using the full volume of the hole:

Three things change the real number:

In the calculator, use the Column tab: enter the hole diameter in inches, the depth in feet and the number of holes, and it totals them for you.

A common rule of thumb is a hole about three times the width of the post, and deep enough to reach below the frost line where the ground freezes. Your local building code and frost depth come first, so check them before you dig.

Bags of Concrete for Footings

Footings are rectangular, so they use the same length × width × depth formula as a slab. Here are two common sizes for a 20 ft run:

Use the Footing tab and enter the depth in inches. Footing sizes for anything structural are set by code, soil and frost depth, not by a rule of thumb.

How Much Extra Should You Buy?

The calculator's bag counts do not include waste, so add 5 to 10% to the volume and then round up. For the 10 x 10 ft patio, 33.33 cu ft plus 10% is 36.67 cu ft, which is 62 bags of 80 lb or 82 bags of 60 lb.

The extra covers dips in the subgrade, forms that bow slightly, spillage and mix left in the wheelbarrow. Running short halfway through is worse than having a few bags left over: the concrete you already placed starts to set, and the joint between old and new concrete is weaker. Many stores accept returns of unopened bags, but check the policy before you rely on it.

Which Bag Size Should You Buy?

Safety and When to Call a Pro

Wet concrete is caustic and can burn skin. Wear waterproof gloves, eye protection and long sleeves, and use a dust mask when you tear open and mix dry bags. Lift with your legs: at 3,600 lb of mix per cubic yard, even a small patio means moving well over a ton of bags.

Call 811 (or your local utility locating service) a few days before you dig so buried lines can be marked. Patios, walkways and post holes are well within DIY range. Foundations, load-bearing footings, retaining walls and driveways that carry heavy vehicles need proper design, reinforcement and often a permit and inspection, so use these numbers to check a quote rather than to replace one.

The Short Answer

Divide your volume in cubic feet by 0.60 for 80 lb bags, 0.45 for 60 lb bags or 0.30 for 40 lb bags, round up, and add about 10%. Run your exact dimensions through the Concrete Calculator, and if your slab sits on a gravel base, work out the stone with how much gravel you need.