How Many Bags of Concrete for a 10x12 Slab?
A 10x12 concrete slab at 4 inches needs about 1.63 yd3 with 10% waste, or 74 80 lb bags. See 4, 5, 6 inch bag counts and cost checks.
A 10x12 concrete slab is 120 square feet. At 4 inches thick, it needs about 1.48 yd3 before waste, 1.63 yd3 with 10% waste, or about 74 common 80 lb bags. The same slab is about 98 60 lb bags or 147 40 lb bags.
Use the Concrete Bag Calculator for exact bag count, price, and waste. If the 10x12 slab is for a shed, also see the Shed Base Concrete Calculator Guide.
Before buying, check the bag's actual yield, the finished thickness and the delivery plan. Bags that weigh the same can contain different products; bag weight alone does not determine how much mixed concrete they produce.
Quick answer
For a 10 ft x 12 ft slab:
| Thickness | With 10% waste | 80 lb bags | 60 lb bags | 40 lb bags |
|---|---|---|---|---|
| 4 in | 1.63 yd3 | 74 | 98 | 147 |
| 5 in | 2.04 yd3 | 92 | 123 | 184 |
| 6 in | 2.44 yd3 | 110 | 147 | 220 |
These are planning counts using common yields of 0.60 ft3 for 80 lb bags, 0.45 ft3 for 60 lb bags, and 0.30 ft3 for 40 lb bags. Always confirm the yield printed on the bag you plan to buy.
Slab thickness, base prep, reinforcement, drainage, frost, anchors, and permits should be confirmed with a qualified local professional.
10x12 slab formula
area = 10 x 12 = 120 sq ft
depth ft = thickness in / 12
volume ft3 = 120 x depth ft
allowance ft3 = volume ft3 x 1.10
order yd3 = allowance ft3 / 27
At 4 inches:
120 x (4 / 12) = 40 ft3
40 x 1.10 = 44 ft3
44 / 27 = 1.629629... yd3
The table displays 1.63 yd3, but bag counts use the unrounded 44 ft3 with allowance. Divide by the product yield, then round up once to whole bags:
44 / 0.60 = 73.333... bags
round up = 74 bags
At 5 inches the volume with allowance is 55 ft3; at 6 inches it is 66 ft3. Use these quantities for the other rows, not rounded yards converted back to cubic feet. The 10% allowance is already included; do not add it again.
For a broader size chart, see Concrete Bags for 100 Square Feet and the Concrete Bag Coverage Chart.
Cost check for a 10x12 slab
Material-only bag cost depends on local shelf price. This table uses the 4 in slab bag counts and hypothetical USD prices, not current store or supplier quotes. Ready-mix pricing uses the unrounded 44 ft3 divided by 27, not the displayed 1.63 yd3.
| Bag size | Bags | Example price | Material check |
|---|---|---|---|
| 80 lb | 74 | $6.50 | $481.00 |
| 60 lb | 98 | $5.25 | $514.50 |
| 40 lb | 147 | $4.25 | $624.75 |
| Ready-mix | 1.63 yd3 displayed | $165/yd3 + $125 delivery | $393.89 |
The USD 125 delivery is already included in the ready-mix example; bag totals are bags only. Neither path includes mixer rental, labor, wheelbarrow time, base gravel, forms, reinforcement, finish, cleanup, tax, or contractor markup. No minimum billable quantity or supplier order increment is assumed. Replace this example with the actual delivered quote and add only charges that are not already included; bag delivery and a ready-mix short-load fee may differ.
Use the Ready-Mix vs Bags Calculator before buying dozens of bags. Crew capacity, access, placement time and actual delivered prices decide the comparison, not a fixed bag-count threshold. For installed-scope pricing, compare the 10x12 Concrete Slab Cost Guide.
What changes the bag count?
| Change | Effect |
|---|---|
| 5 in thickness | Adds about 18 more 80 lb bags than a 4 in slab. |
| 6 in thickness | Adds about 36 more 80 lb bags than a 4 in slab. |
| Uneven base | Low spots can consume extra concrete. |
| Thickened edge | Estimate the edge separately and add it to the slab volume. |
| Bag yield | Fast-setting or specialty mixes may yield differently. |
| Waste factor | The table assumes 10%; choose the allowance for actual measurements, spillage and placement conditions. |
For base depth, see How Much Gravel Under a Concrete Slab. For thickness decisions, see the Concrete Slab Thickness Guide.
Bagged pour workflow
A 10x12 slab at 4 inches can require 74 common 80 lb bags after waste. That is more than a math problem. Plan where bags will stay dry, where the mixer sits, how many bags fit each batch, how water will be measured, and who moves fresh concrete into the forms. A helper who only carries bags may not be enough if the same crew must spread, screed, edge, joint, and clean tools before the mix tightens.
Check the dry load too. Seventy-four 80 lb bags are about 5,920 lb before pallets, packaging, mixer, tools, and water. Pickup payload, trailer capacity, store delivery, unloading time, and jobsite staging can turn a cheap bag price into a difficult pour-day plan.
Ready-mix quote comparison
Ask a ready-mix supplier for a delivered-total quote, not only price per yard. For a 10x12 slab, the usable order may be below the supplier's minimum, so the invoice can include minimum billable yards, short-load fee, delivery, fuel or environmental fees, tax, wait time, and cancellation rules. Compare that total with bags, pallet delivery, mixer rental, extra helpers, and the risk of a slow continuous pour.
Confirm whether the supplier rounds the delivered volume, bills a minimum volume, uses a minimum invoice total, or offers a fixed price for the load. These are different quote models. Do not assume a billed minimum is delivered concrete or add every possible fee on top of an inclusive quote.
If the slab is for a shed, generator, hot tub, or equipment pad, also confirm base depth, reinforcement, anchors, drainage, and finished elevation. Those scope items can matter more than the difference between a bagged material price and a ready-mix material price.
After forms are set
Remeasure the inside length and width after forms are braced. Check thickness at the high side, low side, and corners, then add any thickened edge, ramp landing, apron, or control-joint layout that changes the pour. If the subgrade has low pockets, decide whether they should be corrected with base material or filled with concrete before buying bags.
This final check keeps the bag count connected to the real slab instead of the rough 10x12 label. It also gives a contractor or supplier enough detail to question an order that looks too low. Keep the final dimensions with the receipt so extra bags or returned material can be explained after the pour.
FAQ
How many 80 lb bags for a 10x12 slab at 4 inches?
Plan about 74 common 80 lb bags with 10% waste. Without waste, the math is about 67 bags, but most projects should not buy with zero buffer.
How many 60 lb bags for a 10x12 slab?
At 4 inches thick with 10% waste, plan about 98 common 60 lb bags.
How much ready-mix for a 10x12 slab?
At 4 inches thick, plan about 1.63 yd3 with 10% waste. Ask the supplier about minimum order size, short-load fees, delivery, and chute reach.
Is a 10x12 slab too big for bags?
It can be done with bags, but 74 80 lb bags is a lot of mixing. Compare ready-mix, rental mixer, labor, and schedule before deciding.
Should a 10x12 shed slab be 4 inches thick?
Four inches is a common planning starting point, but shed weight, stored equipment, soil, frost, base prep, and local requirements can change the design.
Next step
Run your exact inputs in the Concrete Bag Calculator, then compare material and installed bids in the Concrete Quote Reviewer. Contractors can prepare a client-facing scope with the Concrete Proposal Kit.
Quote planning next step
Turn this guide into a concrete buying check
Run the matching calculator, then compare ready-mix, bagged concrete, delivery fees, access needs, and quote gaps before you buy materials or approve a contractor number.