A 10 × 10-foot slab with 4 inches of concrete needs 56 bags at 0.60 cu ft per bag, or 62 bags with an example 10% quantity allowance. At 0.45 cu ft per bag, those counts are 75 and 82. Calculate the concrete volume first, divide by the exact product’s stated yield, and round up once at the end.
This is a quantity guide, not a slab, footing or fence design. Concrete thickness excludes the gravel base. Thickened edges, separate footings and post displacement need their own geometry. Use the concrete calculator for rectangular slabs or the larger slab bag chart for more dimensions.
Bag weight is not concrete volume
A bag’s weight describes the packaged material. Its yield describes the approximate volume of concrete it produces when mixed as directed. The cited QUIKRETE Concrete Mix No. 1101 sheet lists these yields.1 They are product-specific estimates, not guaranteed yields for every brand or mix of the same weight.
| No. 1101 bag | Approximate yield (cu ft) | Bags for 1 cu yd net |
|---|---|---|
| 40 lb | 0.3 | 90 |
| 50 lb | 0.375 | 72 |
| 60 lb | 0.45 | 60 |
| 80 lb | 0.6 | 45 |
For this product’s 80-lb yield, 27 / 0.60 = 45 bags per net cubic yard. That is not a pallet count. Confirm package sizes, pallet quantities and the specific product yield at the store.
The formula and rounding order
Rectangular slab cu ft = length (ft) × width (ft) × concrete thickness (in) / 12.
Bags = round up [net cu ft × (1 + allowance % / 100) / yield per bag]. Keep the unrounded volume through the allowance step. Do not round the net bag count first and then apply the allowance.
The 10% column below is a comparison scenario chosen for this guide, not a manufacturer-prescribed allowance. Measure the actual forms and section, then choose an allowance suited to the placement plan. An allowance cannot correct missing geometry or select structural thickness.
4-inch slab bag counts
Calculated scenarios, not thickness recommendations. Counts use the No. 1101 approximate yields above. Net volume is displayed to six decimals but calculations retain full precision.
| Inside slab dimensions | Net cu ft | 80 lb: net | 80 lb: +10% | 60 lb: net | 60 lb: +10% |
|---|---|---|---|---|---|
| 4 × 4 ft | 5.333333 | 9 | 10 | 12 | 14 |
| 8 × 8 ft | 21.333333 | 36 | 40 | 48 | 53 |
| 10 × 10 ft | 33.333333 | 56 | 62 | 75 | 82 |
| 10 × 12 ft | 40.000000 | 67 | 74 | 89 | 98 |
| 12 × 12 ft | 48.000000 | 80 | 88 | 107 | 118 |
| 20 × 20 ft | 133.333333 | 223 | 245 | 297 | 326 |
Three checked examples
1. 10 × 10 ft at 4 inches
Volume = 10 × 10 × 4 / 12 = 33.333333 cu ft. At 0.60 cu ft per bag: 55.555556, rounded up to 56 bags. With example 10% allowance: 36.666667 / 0.60 = 61.111111, rounded up to 62 bags. For 0.45 yield, the corresponding counts are 75 and 82 bags.
2. A 12-inch inside-diameter tube, filled 36 inches high
Radius is 0.5 ft and fill height is 3 ft. Volume = π × 0.5² × 3 = 2.356194 cu ft. At 0.60 yield: 3.926991, rounded up to 4 bags. With example 10% allowance: 2.591814 / 0.60 = 4.319690, rounded up to 5 bags. This models the entire cylinder with no inserted post; any separate base or cap is excluded. See the tube-volume guide.
3. A circular concrete fill around a square post
Quantity example only: a 12-inch diameter concrete zone, 24 inches high, with a measured 3.5 × 3.5-inch square post through its full height. Concrete volume = π × 0.5² × 2 − (3.5 / 12)² × 2 = 1.400657 cu ft. At 0.375 yield: 3.735087, rounded up to 4 bags. With example 10% allowance: 1.540723 / 0.375 = 4.108595, rounded up to 5 bags. A concrete pad below the post is a separate volume. These dimensions are not a post-foundation recommendation. Use the post concrete calculator for the modeled geometry.
Concrete mix is not interchangeable with cement
The No. 1101 sheet describes a pre-blended mixture of cement and aggregates.1 Its bag yield must not be applied to a bag of cement alone, mortar or another mix. Check the product name and yield, not only the bag weight.
Follow the exact product’s mixing and placement directions
The standard Concrete Mix sheet describes mixing before slab placement.1 The cited Fast-Setting Concrete Mix No. 1004 sheet includes a dry-pour method specifically for setting posts, while its slab method places mixed concrete.2 Do not turn that post method into a general slab instruction. Yield math does not establish the right water amount, working time, mixing method or curing plan.
This guide does not prescribe joint spacing, reinforcement, loading time or cure duration. Those depend on the section, product, conditions and design. Use the current package and technical sheet and check applicable project requirements.
Compare bags and delivered concrete using full quotes
Compare rounded bag count × your actual bag price with a supplier’s total quote for the required delivered volume. Include delivery or short-load charges, equipment, transport and labor. A net cubic yard’s 45-bag equivalent at 0.60 yield is a material-volume comparison, not proof of a cheaper or workable placement method. Quantity alone does not create a universal ready-mix threshold.
A checked product link, not a universal pallet count
One example is QUIKRETE 80-lb Concrete Mix, model 110180, at The Home Depot. This is a retailer product link, not a recommendation that this mix fits every job. The manufacturer’s No. 1101 sheet gives approximately 0.60 cu ft per 80-lb bag.1
The retailer listing says 42 bags for a pallet and explicitly warns that pallet counts can differ by location. At the manufacturer’s yield, 42 × 0.60 = 25.2 cu ft, or 0.933333 yd³. A selected 42-bag pallet therefore does not equal a full 27-cu-ft yard. Verify local pallet quantity, product, availability, price and delivery before ordering. Do not infer a universal pallet count from this link.3
FAQ
How many 80-lb bags make a cubic yard?
At 0.60 cu ft per bag, 45 make 27 cu ft of estimated net volume. Check the chosen product yield and any separate allowance.
How much does one bag cover?
Coverage (sq ft) = yield (cu ft) × 12 / thickness (in). At 0.60 yield and 4 inches, one bag covers an estimated 1.8 sq ft. At 0.45 yield it covers 1.35 sq ft. These are geometric estimates, not thickness recommendations.
Should I add a fixed percentage to the bag count?
Choose the allowance separately, apply it to unrounded volume, divide by yield and round up once. The example 10% column is not a rule for every project.
Can I use excavation depth as concrete thickness?
Only if the entire modeled depth is actually filled with concrete. Bedding, base, cover and unfilled space are not concrete volume; inserted posts displace concrete.
Related guides
Concrete calculator | Slab bag chart | 20 × 20 slab yardage | Post concrete calculator
Sources
- QUIKRETE: Concrete Mix No. 1101 (product composition, approximate bag yields and mixing/placement directions)
- QUIKRETE: Fast-Setting Concrete Mix No. 1004 (product-specific post and slab placement methods)
- The Home Depot: QUIKRETE 80-lb Concrete Mix, model 110180 (retailer listing checked October 9, 2026; local pallet-count caveat, not a guaranteed local quote)