On a small job the choice between bagged concrete and a ready-mix truck comes down to three things: volume, access and labour. Material price is only part of it.
How much a bag actually makes
An 80 lb bag of concrete mix yields about 0.6 cu ft. You need 45 of them for one cubic yard. A 60 lb bag yields about 0.45 cu ft (60 per yard), and a 40 lb bag 0.3 cu ft (90 per yard). That is a lot of lifting, mixing and cleaning.
The real cost of bags
Add up the hidden costs of a bag pour:
- Labour. A two-person crew with a mixer realistically places 1–1.5 yards an hour once you include fetching, mixing and placing.
- Consistency. Every batch varies a little in water content. On a large slab this shows as patchy colour and uneven strength.
- Cold joints. If one end starts to set before the other is finished, you get a weak plane through the slab.
- Handling and waste. Split bags, part bags left over and wasted water all add up.
Rules of thumb
| Volume | Usually best |
|---|---|
| Under ⅓ cu yd (post holes, small pads) | Bags |
| ⅓ to 1 cu yd | Bags with a mixer, or a small-load supplier |
| Over 1 cu yd | Ready-mix truck |
| Any volume with poor access | Ready-mix with a line pump or concrete barrow hire |
Short-load fees and minimums
Most US plants add a short-load fee for orders under 3–5 yards, often $50–$150 per missing yard or a flat charge. Even with the fee, a truck often beats bags once you count labour.
Site mixing from cement and aggregate
Mixing from Portland cement, sand and gravel is cheaper per yard than pre-mixed bags, but harder to keep consistent. About 5½ bags of cement per yard gives a typical 3,000 psi mix.
Use the slab calculator with Supply as set to each option to compare them on your own job.
This guide is general information for estimating. It is not engineering, legal or tax advice. Check local codes and your inspector for your project.