Concrete bags vs ready-mix
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Bagged mix is cement and aggregate in a sack. You add the water and place it before the batch gets ahead of you. Ready-mix arrives batched, sold by the cubic yard, and the load has to be placed while it is workable. The break between them is volume, labor, and what the nearest plant does with an order that does not fill a truck. This page does not invent a price per yard or a short-load fee. The yield on the data sheet, and the volume this site already calculates, are the parts that do not move.
The yield that sets the bag count
QUIKRETE Concrete Mix, product 1101, publishes yields on its data sheet: about 0.30 cubic feet for a 40 lb bag, 0.375 for 50 lb, 0.45 for 60 lb, 0.60 for 80 lb, and 0.675 for 90 lb. The sheet says the mix meets ASTM C387, the specification for packaged, dry, combined materials for concrete. A cubic yard is 27 cubic feet. Dividing 27 by those yields is the bag count per yard, before you round a partial bag up.
| Bag | Yield on the sheet | Bags per cubic yard | 12×24×4 in slab (3.56 yd³, 96.00 ft³) |
|---|---|---|---|
| 80 lb | 0.60 ft³ | 27 ÷ 0.60 = 45 | 96 ÷ 0.60 = 160 bags |
| 60 lb | 0.45 ft³ | 27 ÷ 0.45 = 60 | 96 ÷ 0.45 = 213.33, which the bag calculator rounds up to 214 |
| 40 lb | 0.30 ft³ | 27 ÷ 0.30 = 90 | 96 ÷ 0.30 = 320 bags |
| 50 by 12 ft driveway, 4 in | 7.41 yd³ on the driveway calculator | 7.41 × 45 = 333.45 bags of 80 lb | 334 bags if you round the partial bag up, before waste |
The 160, 214, and 320 counts are the bag calculator for that slab, the same 3.56 cubic yards and 96.00 cubic feet as the concrete calculator. The driveway row is the driveway calculator: 50 by 12 feet at 4 inches is 7.41 cubic yards, and 7.41 × 45 is the 80 lb count. If the bag in your hand prints a different yield, use that yield. Waste is extra. The concrete calculator says to add about 5 to 10 percent yourself. It is not hidden in the 160. Ten percent on the 7.41 yard driveway is the 8.15 yards that driveway page already shows.
What the mixing actually takes
The data sheet is the labor, in units rather than a guessed hourly rate. Start each 80 lb bag with about 6 pints of water. The final water is about 6 to 9 pints. The slump, if you check it, is 2 to 3 inches. A mixer needs at least 1 cubic foot of capacity per 80 lb bag in the batch, so a small mixer is one bag at a time. The sheet also allows a tub and a hoe: no dry pockets, and no standing water. The 12 by 24 slab is 160 of those batches in a one-bag mixer, placing 3.56 cubic yards. The sheet’s slab method is full-depth placement, control joints about 1 inch deep every 6 to 8 feet, and curing for 5 days at 70°F or higher, or 7 days at 50 to 70°F.
The 7.41 yard driveway is 334 batches before waste. Concrete from the first hour will not wait while you mix the last hour, which is why that volume is a truck conversation. The sheet lists driveway repairs, sidewalks, patios, and floor slabs, for pours 2 inches or thicker. A repair fits the bag. A full driveway is the plant. Typical results on the sheet are 2,500 psi at 7 days and 4,000 psi at 28 days, at about 140 lb per cubic foot. Those are this packaged mix tested to ASTM C39, not a plant design and not a code minimum. If the drawing names a mix, order that mix.
The ready-mix side, without a fake price
Ask the plant for a price per yard, how long the truck will wait, and what they charge if you are not ready. Then ask the short-load question directly. A short load is an order below a full truck or below the plant’s minimum, billed at a higher price per yard, a flat charge, or a minimum quantity. This site’s driveway calculator uses a 10 cubic yard truck as a planning capacity, not a price. At that assumption 7.41 yards is one truck and still short of 10. Whether that costs extra is the dispatcher’s number. The calculator already says it does not price a short load.
With the quote in hand, multiply the bag count by the sack price you can actually buy, and add delivery or a mixer rental if you will pay either. Multiply the ready-mix yards, including the waste you added, by the price per yard, and add the short-load charge and any pump or extra chute. Compare the same yards. Do not compare 160 bags with a 5 yard minimum, or neat volume with a quote that already includes waste.
Where the line usually falls
A few post holes, a landing, and the 12 by 24 pad are bag work if you can mix them. The post hole calculator and the column calculator are those small volumes. The data sheet describes setting a post and says to follow the local footing rule for a load-bearing one. Add the holes before you decide: one sonotube is a sack or two, and twenty of them may be a truck.
A driveway or a garage slab tips the other way because the limit becomes cold joints, not the price of a sack. The slab calculator is the flat volume. The driveway calculator adds the truck count. The phone call is the 7.41 yards, the price per yard, and the charge for being under a full load. A bag of portland cement is not this premix. The cement calculator is the binder only. Self-leveling compound is a flooring product, not a 4 inch driveway.
Weight is a check, not a price. These concrete pages start at 2,400 kg/m³, about 2.02 short tons per cubic yard, as a planning default. The data sheet’s unit weight is about 140 lb per cubic foot, which is 3,780 lb per cubic yard. Same neighborhood, different calculation. Use the plant ticket for the truck and the bag count for the sacks.
Sources
- QUIKRETE Concrete Mix, product 1101, data sheet. Yields, mixing water, mixer capacity, ASTM C387, and the typical strength table. No prices.
- The 3.56 yard slab and the 7.41 yard driveway are the worked examples on this site’s bag calculator, concrete calculator, and driveway calculator. The 10 yard truck is that driveway page’s planning assumption.
Frequently asked questions
How many 80 lb bags are in a cubic yard?
Forty-five, if the bag yields 0.60 cubic feet. A cubic yard is 27 cubic feet, and 27 ÷ 0.60 = 45. That is the yield on the Quikrete Concrete Mix data sheet for product 1101, and it is the yield this site’s bag calculator already uses. The same sheet lists 0.45 cubic feet for a 60 lb bag, which is 60 bags per yard, and 0.30 cubic feet for a 40 lb bag, which is 90 bags per yard. Check the bag in your hand before you treat 45 as universal.
How many bags is the 12 by 24 foot slab?
The bag calculator’s worked example is 12 feet by 24 feet by 4 inches: 96.00 cubic feet, 3.56 cubic yards. At 0.60 cubic feet per bag that is 160 bags of 80 lb mix. At 0.45 cubic feet it is 214 bags of 60 lb mix. At 0.30 cubic feet it is 320 bags of 40 lb mix. Those counts are the neat volume. The concrete calculator’s waste note of 5 to 10 percent is extra, and it is not hidden in the 160.
Is a 7 yard driveway a bag job?
The concrete driveway calculator’s 50 by 12 foot drive at 4 inches is 7.41 cubic yards. At 45 bags per yard that is 333.45 bags of 80 lb mix, which rounds up to 334 bags before waste. That is a mixer crew, not a Saturday with a wheelbarrow. It is also under a 10 yard planning truck, so it is exactly the size of order where you should ask the plant about a minimum load and a short-load charge. This page does not know that charge.
What is a short load?
A short load is an order below the plant’s full truck, or below the minimum they will deliver at the normal price per yard. Plants handle that with a higher price per yard, a flat charge, or a minimum billing quantity. The amount is local. The driveway calculator on this site counts trucks at a 10 yard planning capacity and says it does not price a short load. Ask the dispatcher for three numbers: the price per yard, the minimum yards they will send, and any short-load charge on an order the size of yours.
How do I compare the cost without a national price?
Price the bags you can actually buy, multiply by the bag count, and add the mixer, the water, and the hours. Then price the ready-mix quote for the same yards, including the short-load charge and any waiting time. The cheaper line is the break-even for that pour, in your town, this month. A price printed here would be fiction. The arithmetic that is not fiction is 45 bags of 80 lb mix per cubic yard at a 0.60 cubic foot yield.
Does the Quikrete sheet cover a whole driveway?
The product-use list on data sheet 1101 includes driveway repairs, sidewalks, floor slabs, patios, footings, and pours 2 inches thick or more. It does not say the bag is a substitute for a specified ready-mix driveway. The typical strengths on that sheet are 2,500 psi at 7 days and 4,000 psi at 28 days, tested as that packaged mix. A plant mix is a different product with its own ticket. Match the spec you were given, not this paragraph.
Are bags of cement the same as bags of concrete?
No. Concrete mix is cement plus the sand and stone, and you add water. A bag of cement is the binder only. The cement calculator on this site is the binder. The bag calculator is the premix. Using the cement page to order a slab will under-buy the stone and sand, and using the premix page to order a mortar job will buy aggregate you did not want.