How much concrete for a 12×12 slab?
A 12 × 12 ft slab 4 inches thick takes 1.78 cubic yards of concrete (48 cubic feet). With 10% extra that is 1.96 cubic yards — order 2 yards — or 88 bags of 80 lb mix (118 of 60 lb).
How to work it out
- 12 ft × 12 ft = 144 sq ft
- 144 sq ft × 4 in ÷ 12 = 48 cu ft ÷ 27 = 1.78 cu yd
- + 10% extra = 1.96 cu yd = 52.8 cu ft
- 52.8 cu ft ÷ 0.6 cu ft per 80 lb bag = 88 bags
At 144 square feet, a 12×12 is a roomy patio, a pad for a 10×12 shed with a small apron, or the floor of a gazebo. It is the size where the bag count passes 80 and most people start pricing a truck.
Adjust for your project
More options: Extra · Price
- Or bags of mix (incl. extra)
- 88 bags · 80 lb bag
- Concrete before the extra
- 1.78 cu yd (48 cu ft)
- Slab area
- 144 sq ft
- Weight of the concrete (≈ 145 lb/cu ft)
- 6,960 lb (3 tons)
- 88 bags is a lot of mixing. Compare a ready-mix delivery (ask about minimum loads and short-load fees) with the bags vs ready-mix calculator.
- Total to buy counts this as ready-mix. Switch “How will you buy it?” to bags if you are mixing it yourself.
- Plan control joints about 1 in deep every 6–8 ft (Quikrete’s guidance) so shrinkage cracks follow your lines.
12×12 slab by thickness (10% extra included)
| Thickness | Concrete to order | Or bags of mix (incl. extra) | Weight of the concrete (≈ 145 lb/cu ft) |
|---|---|---|---|
| 3.5 in | 1.71 cu yd | 77 bags | 6,090 lb |
| 4 in | 1.96 cu yd | 88 bags | 6,960 lb |
| 5 in | 2.44 cu yd | 110 bags | 8,700 lb |
| 6 in | 2.93 cu yd | 132 bags | 10,440 lb |
Why 2 yards is the number to order
The math lands almost exactly on a round number: 1.78 yards in the forms, 1.96 with the usual 10% allowance. Ordering 2 yards gives you a small cushion without paying for concrete you will have to dump. Two yards is still a small load for a ready-mix plant, so ask about the minimum and any short-load charge when you call — on some days a smaller “mini-mix” supplier or a trailer rental from a local yard is the better fit.
Doing it with bags means about 88 of the 80 lb size, roughly 7,000 lb of dry mix and somewhere around 66 gallons of water at Quikrete’s starting rate of 6 pints per bag. That is a full day for two or three people with a rented mixer, and the first batches will be setting up while the last ones are mixed. Plan the pour in sections divided by form boards if you go this way.
Joints and slope
Split the slab into four 6 × 6 ft panels with one control joint each way, cut about an inch deep. If it is a patio against the house, slope the forms away from the wall; a common target is about ⅛ to ¼ in per foot, so the far edge sits 1½ to 3 in lower over 12 ft. The same footprint in footings is a different question — see the footing volume calculator — and a slab twice as wide is worked through on how much concrete for a 12×24 or 20×20 slab.
Different size? Use the full Concrete Calculator.
What you’ll need
- Portable electric concrete mixerPremium price
A small drum mixer turns a long day of hand-mixing into batches of two or three 80 lb bags. Check the drum size against the bag count you need.
See options on Amazon (opens in a new tab) - Bull float with handleMid-range price
Smooths and levels a slab you can’t reach across, right after screeding. Rent or buy one for anything wider than about 6 ft.
See options on Amazon (opens in a new tab) - Concrete edger and groover setBudget price
The edger rounds slab edges so they don’t chip; the groover cuts control joints while the concrete is still soft.
See options on Amazon (opens in a new tab)
As an Amazon Associate we earn from qualifying purchases. Links to products are affiliate links — they cost you nothing extra and help keep these calculators free.
Frequently asked questions
How much concrete for a 12×12 slab 6 inches thick?
2.67 cubic yards, or 2.93 cubic yards with 10% extra (132 bags of 80 lb).
How many 80 lb bags of concrete for a 12×12 slab 3½ inches thick?
About 77 bags with 10% extra, for a slab formed with 2×4s.
How much concrete for a 12×12 slab with no extra?
Exactly 1.78 cubic yards at 4 inches, or 80 bags of 80 lb. Don’t order it this tight.
Other common sizes
- How much concrete for a 10×10 slab — 1.36 cu yd with 10% extra (62 bags of 80 lb)
- How much concrete for a 20×20 slab — 5.43 cu yd with 10% extra at 4 in
- How many yards of concrete for a 24×24 slab — 7.82 cu yd with 10% extra at 4 in
- How much concrete for a 30×40 slab — 16.3 cu yd with 10% extra at 4 in
- How many bags of concrete for a 4×4 slab — 10 bags of 80 lb (14 of 60 lb), 4 in thick
- How many bags of concrete for an 8×8 slab — 40 bags of 80 lb, 4 in thick
- How much concrete for a 10×12 shed — 1.63 cu yd with 10% extra; about 2 cu yd with a thickened edge
Sources
- Quikrete Concrete Mix (No. 1101) data sheet (opens in a new tab) — Yields: 40 lb ≈ 0.30, 50 lb ≈ 0.375, 60 lb ≈ 0.45, 80 lb ≈ 0.60, 90 lb ≈ 0.675 cu ft; unit weight ≈ 140 lb/cu ft; for pours 2 in thick or more; 6–9 pints of water per 80 lb bag; control joints every 6–8 ft; cure 5 days at 70 °F or above, 7 days at 50–70 °F; protect from freezing for 48 hours.
- NRMCA Concrete in Practice 31 — Ordering Ready Mixed Concrete (opens in a new tab) — Truck mixers carry 8 to 12 cubic yards (about 6 to 9 m³); order 4–10% more than the plan estimate; a loaded truck weighs about 80,000 lb; fresh concrete can cause severe chemical burns.
- NRMCA Concrete in Practice 2 — Scaling Concrete Surfaces (opens in a new tab) — Order air-entrained concrete (about 6% air) for exterior slabs exposed to freezing and de-icers; avoid de-icing chemicals in the first winter.
- Iowa DOT Instructional Memorandum 340 — Weight per cubic foot, yield and air content of concrete (opens in a new tab) — Normal-weight concrete is typically 140–150 lb per cu ft at 5 to 8 percent air.
- OSHA 3351 — Preventing Skin Problems from Working with Portland Cement (opens in a new tab) — Wet portland cement can cause caustic burns that may not hurt at first and in severe cases reach the bone.
- NIST Handbook 44, Appendix C — General Tables of Units of Measurement (opens in a new tab) — 1 cubic yard = 27 cubic feet; 1 cubic foot = 1,728 cubic inches.