Hardscape · Guide
Bagged Concrete vs Ready-Mix: The Break-Even Point
Below about a cubic yard, bags usually win. Above two, the truck nearly always does. In between, it comes down to a short-load fee and how you feel about lifting two tons.
Concrete can arrive two ways. You can buy it dry in bags, add water and mix it yourself. Or you can order it already mixed, delivered in a truck and poured down a chute. For a fence post, bags are the obvious answer. For a driveway, the truck is. Most garden projects, such as shed bases, small patios and footings, fall in the uncertain middle.
How much is in a bag
A bag of concrete mix makes less than people expect.
| Bag | Mixed concrete | Bags per cubic yard |
|---|---|---|
| 40 lb | 0.30 cu ft | 90 |
| 50 lb | 0.375 cu ft | 72 |
| 60 lb | 0.45 cu ft | 60 |
| 80 lb | 0.60 cu ft | 45 |
A cubic yard is 27 cubic feet. At 0.6 cubic feet a bag, it takes 45 bags of the largest size to make one. Those 45 bags weigh 3,600 pounds dry, and about 4,000 pounds once water is added.
To put a yard in context, it is a slab 9 feet by 9 feet at 4 inches thick. That is a small shed base.
The cost comparison
Bagged concrete costs more per cubic yard than ready-mix, often about twice as much. But ready-mix plants set their prices around full trucks, which carry 8 to 10 yards. Order only one or two and most plants add a short-load fee, a fixed charge for sending out a mostly empty truck.
So the comparison has the same shape as any bags-versus-bulk decision:
And the break-even volume is:
where the bag price per yard is 45 times the price of an 80 pound bag.
An example. The prices here are for illustration, so use your own. Say 80 pound bags are $6.50, ready-mix is $165 a yard, and the short-load fee is $150.
- Bag price per yard: 45 × 6.50 = $292.50
- Saving per yard with ready-mix: 292.50 − 165 = $127.50
- Break-even: 150 ÷ 127.50 = 1.2 cubic yards
Below 1.2 yards, bags are cheaper at these prices. Above it, the truck is. Change the short-load fee to $250 and the break-even moves to about 2 yards. That one fee does more to decide the answer than anything else, so ask for it when you call for a quote.
The labor that the price leaves out
Cost per yard is half the story. The other half is what it takes to turn bags into a slab.
Lifting. Every bag is lifted at least three times: into the vehicle, out of it, and into the mixer. For one yard in 80 pound bags, that is 45 bags and more than 10,000 pounds of lifting in total.
Mixing. A rented drum mixer handles two or three 80 pound bags at a time. One yard is 15 to 20 batches. Each batch is loaded, watered, mixed for a few minutes, dumped and wheeled to the form.
Time pressure. Concrete starts to stiffen within an hour or so of mixing, faster in warm weather. On a slab, the first batches are setting while the last are still in the bag. Fresh concrete poured against concrete that has already begun to set forms a weak seam called a cold joint. This is the real limit on hand-mixed pours, and it is why slabs much over a yard are hard to do well from bags without several people.
Consistency. Every batch gets its own measure of water. Too much water makes concrete easier to pour and much weaker when cured. Twenty batches means twenty chances to get it slightly different.
Ready-mix removes all of that. The whole pour arrives at once, mixed to a specified strength, and your work is to spread, level and finish it.
What the truck asks of you
Ready-mix is not effortless. It moves the pressure to a different place.
- You must be ready. Forms built and braced, base compacted, reinforcement in place, tools laid out, helpers present. The truck will not wait long, and most plants charge for waiting time beyond a short allowance.
- The truck has to reach the pour. A chute reaches about 10 to 15 feet from the back of the truck. Beyond that you are wheelbarrowing, fast, or paying for a pump.
- The truck is heavy. A loaded mixer can weigh over 60,000 pounds. Keep it off lawns you care about, septic systems, and thin driveways.
- It all comes at once. A yard and a half of concrete has to be placed and leveled within about an hour. Two or three people is a sensible minimum.
- You pay for what you order. Order too little and you have a real problem. Order a bit over, and have somewhere useful for the extra to go, such as a small pad or stepping-stone forms.
The middle options
Between a pallet of bags and a full-size truck there are other choices, depending on where you live.
Mix-on-site trucks. Also called volumetric mixers. They carry the dry ingredients separately, mix at your curb, and charge for exactly what is poured. There is usually no short-load fee, though the price per yard is higher. For 1 to 3 yards they are often the best answer.
Trailer loads. Some suppliers and rental yards sell ready-mixed concrete in a towable trailer holding about a yard. You tow it home and pour it yourself. You need a vehicle rated to tow two tons or more, and no time to waste.
A rented mixer and a crew of friends. For about a yard, a towable mixer, a pallet of bags delivered to the driveway, and three people working steadily will do it in an afternoon.
A rule of thumb by project
| Project | Typical volume | Usually best |
|---|---|---|
| Setting fence or deck posts | Under 0.75 cu yd, in separate holes | Bags |
| Small repairs, steps, a mailbox post | Under 0.25 cu yd | Bags |
| Shed base, 8 × 10 ft at 4 in | 1.0 cu yd | Either. Compare the fee |
| Patio, 12 × 12 ft at 4 in | 1.8 cu yd | Ready-mix or mix-on-site |
| Driveway or large slab | 5 cu yd and up | Ready-mix |
Post holes are a special case. The total may be half a yard or more on a long fence, but each hole is poured separately and none is time-critical. Fast-setting mix goes into the hole dry and is watered in place. Bags are the right tool for that job at almost any quantity.
Getting the volume right first
Whichever you choose, start from an accurate volume.
Add 5 to 10% for uneven ground and spillage. With bags, the extra is cheap, and unopened bags can usually be returned. With ready-mix, the extra is your margin of safety against the worst outcome, which is running out with the pour half done.
The concrete calculator gives the volume, the bag count for each size and the ready-mix order together, and compares the two costs if you enter your prices and the short-load fee.
Questions to ask the ready-mix plant
- What is the price per yard for the mix I need?
- What is the minimum order, and what is the short-load fee below it?
- How much unloading time is included, and what does waiting cost after that?
- How far can the chute reach, and can the truck get to my site?
- What strength do you recommend for this use? Tell them what you are pouring. They will know.
- Is there a charge for delivery on a Saturday?
Five minutes on the phone with those six questions gives you everything the break-even formula needs.
Written and checked by Bertha
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