How Many Bags of Concrete Make a Cubic Yard, and When to Order Ready-Mix

Bags per cubic yard: the short answer

A bag of concrete mix is sold by weight but used by volume. What matters is its yield: the volume of finished concrete one bag makes once water is added. A cubic yard is 27 cubic feet, so bags per yard is simply 27 divided by the yield. The yields below are the ones the concrete calculator uses, and they match the approximate yields Quikrete publishes on its Concrete Mix data sheet.

To reproduce the bag column in the concrete calculator, use the Slab / Footing tab with length 27 ft, width 1 ft, thickness 12 in, one slab, waste factor 0%, and switch the bag size. The last column is just bags × bag weight, and it is the same 3,600 lb whichever size you buy: smaller bags do not mean less lifting, only more trips. The same data sheet also lists 50 lb (0.375 ft³) and 90 lb (0.675 ft³) bags, which work out to 72 and 40 bags per yard; the calculator's bag selector does not offer those two sizes, so divide by their yield yourself. Fast-setting and specialty mixes have their own yields, which is another reason to read the bag.

Worked example: a 10 × 10 ft slab at 4 in

Worked example: ten fence-post holes

Quikrete's fence-post instructions suggest a hole about three times the post's diameter, dug to one-third of the post's overall height. For a 4×4 (actually 3½ in square) that is roughly a 10 in hole, and for a 9 ft post a 3 ft depth. In the calculator, use the Round Column tab: diameter 10 in, height 3 ft, 10 columns, 10% waste. It returns 16.4 ft³ before waste, 18 ft³ with it, 0.67 yd³, and 60 × 40 lb, 40 × 60 lb or 30 × 80 lb bags.

One thing to know: the calculator treats each hole as solid concrete and does not subtract the post. A 3½ in square post standing 3 ft deep takes up about 0.26 cubic feet per hole, or about 2.6 cubic feet across ten holes, which is a little over four 80 lb bags. On post jobs that difference simply becomes extra margin, which is useful, because hand-dug holes are rarely as neat as the number you typed in.

Worked example: a set of pad footings

A pad footing is a short, thick slab, so it goes in the Slab / Footing tab. Take eight pads, each 2 ft × 2 ft × 12 in deep, at 10% waste (enter length 2, width 2, thickness 12, number of identical footings 8). The calculator returns 32 ft³ before waste, 35.2 ft³ with it, 1.3 yd³, and 118 × 40 lb, 79 × 60 lb or 59 × 80 lb bags. These dimensions are only an example of the arithmetic. Real footing sizes and depths are structural and frost-related, and must come from your plans, an engineer or your local code.

Bags or ready-mix: where the crossover sits

All three examples above land between about two-thirds of a yard and a yard and a half, which is exactly the range where the decision is genuinely close. The calculator page's rule of thumb is about one cubic yard. Rather than trust any single number, weigh these four things against your own job.

• Weight and labor. Every cubic yard of bagged mix is 3,600 lb of dry material that someone has to handle more than once, before any water goes in or any mixing starts. That is fine for a few post holes and a lot of work for a patio.
• Time to place. NRMCA notes that concrete normally sets and hardens within two to eight hours after mixing. Hand-mixed batches come in one at a time, so a large bagged pour can have its first batches stiffening while the last are still being mixed, which risks cold joints.
• Consistency. A truck delivers one uniform mix, made to the strength and slump you order. Dozens of separate bag batches are only as consistent as the person measuring the water.
• Truck size and small loads. NRMCA gives truck mixer capacity as 8 to 12 cubic yards, so a pour of one or two yards is a small fraction of a load. Ask your local supplier whether it has a minimum order or a small-load charge; a fixed charge spread over very few yards can raise the effective price per yard sharply, which is what keeps bags competitive on small pours.

You can find your own crossover with two quotes and no guesswork. Price both options for the same volume, including the waste allowance:

Then add what the price comparison leaves out: mixer rental, an extra pair of hands, and whether the truck can actually reach the forms. NRMCA points out that a loaded concrete truck weighs about 80,000 lb and may not be able to cross loose dirt or residential curbs, so a backyard pour may also need a pump or wheelbarrows, which changes the comparison again.

Thickness drives everything, so get it from a source

Volume rises in direct proportion to thickness, so a 6 in slab takes half again as much concrete as a 4 in one. Manufacturer guidance gives these common starting points; your plans and local code take precedence.

For comparison, the same 10 × 10 ft slab at 6 in instead of 4 in comes out at 2.04 yd³ and 92 × 80 lb bags with 10% waste, which moves it from borderline to a clear ready-mix job.

Where concrete estimates go wrong

• Ordering exactly what the math says. NRMCA recommends ordering 4 to 10 percent more than the volume calculated from plan dimensions, to cover waste, over-excavation and other contingencies. The calculator defaults to 10%, the top of that range. Running out mid-pour is far more expensive than a few spare bags.
• Assuming the subgrade is flat. NRMCA's own example: an extra ⅛ in on a 4 in slab is a 3 percent shortage. Low spots add up faster than that. If the 10 × 10 ft slab averages 4½ in instead of 4 in, it needs 37.5 ft³ before any spillage, which is more than the 36.7 ft³ that a 4 in estimate with 10% waste provides. NRMCA also lists bulging forms and settlement on irregular subgrade among the usual causes, so brace the forms, compact the base and check depth in several places.
• Rounding bags down. The calculator always rounds the bag count up to a whole bag, as Quikrete's online calculator also does. Keep it that way; a partial bag is still a whole bag at the store.
• Mixing bag sizes without converting. If you buy some 60 lb and some 80 lb bags, count by volume (yield) rather than by number of bags. Two 60 lb bags (0.90 ft³) are not two 80 lb bags (1.20 ft³).
• Adding water to make it easier to place. NRMCA warns that excess water can cause segregation, delay setting, increase the potential for cracking, and reduce strength and durability. Use the water range printed on the bag.