Bagged concrete is sold by weight, but the number that matters on site is volume. How many cubic feet are in a bag of concrete decides how many bags a footing, pad or repair needs, and the answer is printed on every bag as its yield. A 60 pound bag produces 0.45 cubic feet, and the other common sizes scale from there in predictable steps.
Knowing these volumes turns a guess into an estimate you can defend. The same figures cover everything from fence post footings to decorative concrete floor and wall tiles, because coverage always comes back to the volume of the mix and the depth of the pour. This article walks through the per-bag volumes, the coverage at common depths and the quick conversions that keep a project on budget.
Cubic Feet per Bag by Size
Manufacturers measure each batch so the printed yield holds up on site. The standard sizes run from 10 pound repair bags to 90 pound contractor bags, and the volume climbs with the weight. The table below lists the common sizes, their wet volume and the number of bags needed to make one cubic foot.
| Bag size | Cubic feet per bag | Cubic yards per bag | Bags per cubic foot |
|---|---|---|---|
| 10 lb | 0.075 | 0.0028 | 13.33 |
| 20 lb | 0.15 | 0.0056 | 6.67 |
| 40 lb | 0.30 | 0.011 | 3.33 |
| 50 lb | 0.375 | 0.0139 | 2.67 |
| 60 lb | 0.45 | 0.0167 | 2.22 |
| 80 lb | 0.60 | 0.0222 | 1.67 |
| 90 lb | 0.675 | 0.025 | 1.48 |
Why 0.45 cubic feet for a 60 pound bag
The 60 pound bag is the reference point most people learn first. It yields 0.45 cubic feet, which equals 0.017 cubic yards and covers 1.8 square feet at a standard 3 inch depth. One cubic foot of concrete needs about 2.2 bags of this size, so a small repair mix rounds to three bags once waste is included.
The 20 pound rule
Most bagged mixes produce roughly 0.15 cubic feet for every 20 pounds of dry mix. A 40 pound bag doubles that to 0.30 cubic feet, a 60 pound bag triples it to 0.45, and an 80 pound bag delivers 0.60. If a brand prints a slightly different yield, the ratio still holds within a few percent, so the table stays useful across suppliers.
Bag labels print the yield for a reason: the physical bag is packed by weight, and dry mix settles in transit, so eyeballing the bag tells you nothing about volume. Read the fine print on the front panel, usually stated as a fraction like 0.45 cu ft, and use that figure for every count on the project.
Yield describes the mix in the bag, not the quality of the pour. In tight spots with heavy rebar, crews use poker vibrators to consolidate concrete in congested reinforced concrete members, and the same care applies to any placement where voids could hide.
Bags per Cubic Foot and per Cubic Yard
A cubic yard is a cube three feet long, three feet wide and three feet deep, which works out to 27 cubic feet. That single number connects bag counts to ready-mix quantities and makes both easy to compare.
Converting between units
- Find the total volume of the pour in cubic feet.
- Divide by the yield per bag to get the bag count.
- Divide cubic feet by 27 to get cubic yards, or multiply cubic yards by 27 to go the other way.
Worked example: one cubic yard
One cubic yard needs 45 eighty-pound bags, since 27 divided by 0.60 equals 45, or 60 sixty-pound bags, since 27 divided by 0.45 equals 60. A ready-mix truck delivers a full yard or more, which is why bagged concrete makes sense only for volumes under roughly half a yard.
Estimators lay these conversions out in a standard worksheet. A concrete estimating worksheet with blank columns for dimensions, volume and bag count keeps the arithmetic visible and easy to check before you order.
Comparing bags against a truck comes down to the same conversion. A 1 cubic yard minimum order equals 27 cubic feet, or about 45 eighty-pound bags. If the project needs less than that, the truck leaves expensive concrete in the drum and the cleanup is yours; bags keep the pour exactly the size of the job.
Square Foot Coverage at Common Depths
Coverage depends on depth, not just bag size. The same 0.45 cubic feet covers 5.4 square feet at one inch, 1.8 square feet at three inches and 1.35 square feet at four inches. Doubling the depth halves the coverage, because the same volume is spread thinner or thicker over the area.
| Bag size | Coverage at 1 in | Coverage at 3 in | Coverage at 4 in |
|---|---|---|---|
| 40 lb (0.30 cu ft) | 3.6 sq ft | 1.2 sq ft | 0.9 sq ft |
| 60 lb (0.45 cu ft) | 5.4 sq ft | 1.8 sq ft | 1.35 sq ft |
| 80 lb (0.60 cu ft) | 7.2 sq ft | 2.4 sq ft | 1.8 sq ft |
Depth drives the bag count
A slab at 4 inches uses four times the concrete of a 1 inch topping over the same footprint. Most walkways and patios spec at 3 to 4 inches, while footings and piers go deeper. The surface area stays the same; only the volume changes, and the bag count follows the volume.
For a concrete example, a 12 inch diameter post hole 24 inches deep holds about 1.6 cubic feet, so a single setting takes roughly four 60 pound bags. A 3 inch thick walkway 3 feet wide and 10 feet long uses 7.5 cubic feet, or 17 eighty-pound bags. Working through one small project in cubic feet makes the next estimate faster.
When coverage figures mislead
Coverage numbers assume a flat, uniform pour. Low spots eat extra mix, and spillage or over-vibration adds 5 to 10 percent waste. Rough, absorbent bases drink more water and can pull more material, which is one reason crews are careful when they pour new concrete over an old concrete surface.
How Bag Volume Is Measured and Why It Varies
The printed yield is the wet volume after mixing with the recommended water, not the dry volume sitting in the bag. Dry mix settles in storage, so the physical size of the bag is a poor guide. Weight and the manufacturer’s test data are the reliable numbers.
Moisture and measurement
Ready-mix concrete weighs about 133 pounds per cubic foot in the dry state, or roughly 3,600 pounds per cubic yard. A bag’s yield assumes standard moisture content; damp bags compact and can pour short. Store bags off the ground, keep them covered, and use the freshest stock you can find.
Brand differences
Two brands can print different yields for the same bag weight. The gap usually comes from aggregate grading and cement content, so read the yield line on the bag rather than trusting the weight alone. After the pour, verification matters as well: slump checks and cylinder sampling, covered under post-concrete inspection and testing routines, confirm the mix performed the way the bag promised.
Density explains most of the spread. Standard concrete mix packs at roughly 133 pounds per cubic foot dry, so a 60 pound bag works out to about 0.45 cubic feet by weight alone. High-density mixes with heavier aggregates, used for radiation shielding or ballast, deliver less volume per bag, while lightweight mixes deliver more.
Ready-Mix Bags in Practice
When bags beat the truck
- The pour is under half a cubic yard.
- A delivery truck cannot reach the site.
- The work happens in phases over several days.
- The budget needs exact quantities with no leftover yardage.
Double-check with a calculator
An online concrete calculator converts bag size, footprint and depth into a bag count in seconds. Enter the slab dimensions, pick the bag weight and compare the result with your hand math; the two should agree within one bag.
A typical bagged pour for a fence line shows the pattern: eight post holes at 1.6 cubic feet each come to 12.8 cubic feet, or 29 sixty-pound bags. Bought by the pallet, that quantity usually arrives on a single pallet, and mixing eight settings over a weekend beats renting a mixer truck for a quarter yard of concrete.
Once a project outgrows bagged mix, the analysis of prestressed concrete over reinforced concrete explains why some members are precast and tensioned in a plant rather than poured in place.
Putting the Numbers to Work
A quick estimating checklist
- Confirm the bag size and its printed yield in cubic feet.
- Compute the total volume of the pour in cubic feet.
- Divide to get the bag count and round up.
- Add 5 to 10 percent for waste and test patches.
Match the mix to the job
Not every bag is the same product. The difference between lean concrete and normal concrete changes the yield math, because lean mixes carry less cement and more aggregate and are used for leveling beds and protection layers rather than structure. Check the label before assuming the yield matches a standard bag, then order one extra bag per ten to be safe.
Keep a small notebook or a phone note with the yield of the bag you use most. One line with the bag weight, the cubic feet per bag and the date of purchase is enough to estimate the next pour without re-reading the label.