Guide · Concrete
How Much Concrete Do I Need for a 12×12 Slab?
A 12×12 slab poured 4 inches thick needs 1.78 cubic yards of concrete — about 48 cubic feet. That’s the classic size for a modest patio or hot-tub pad. Add a 10% waste allowance for uneven subgrade and spillage, and plan for 1.96 cubic yards. Mixing bags instead of ordering ready-mix? That’s 107 sixty-pound bags before waste, or 118 with waste built in.
Those are the headline numbers. Below is the exact math so you can verify it, a chart covering other common slab sizes, and guidance on thickness, bags vs. ready-mix, and cost. If you’d rather skip the arithmetic, use our free concrete calculator — enter your slab dimensions and it returns cubic yards plus 40-, 60-, and 80-lb bag counts in seconds.
Get cubic yards and bag counts for your exact slab dimensions — free, no sign-up.
Use the interactive concrete calculator →Before waste. With a 10% allowance: 1.96 yd³, or 118 sixty-pound bags.
The math, step by step
= 12 ft × 12 ft × (4 ÷ 12) ft = 48 ft³
Cubic yards = 48 ÷ 27 = 1.78 yd³
- Convert thickness to feet. Four inches is 4 ÷ 12 = 0.333 ft.
- Multiply. 12 × 12 × 0.333 = 48 cubic feet.
- Convert to cubic yards. There are 27 cubic feet in a yard: 48 ÷ 27 = 1.78 yd³.
- Add waste. 1.78 × 1.10 = 1.96 cubic yards to order.
- Convert to bags. A 60-lb bag yields about 0.45 ft³: 48 ÷ 0.45 = 106.67, round up to 107 bags. With waste: 52.8 ÷ 0.45 = 117.33, round up to 118 bags.
Concrete needed for common slab sizes
Bag counts below are before waste and assume the standard 0.45 ft³ yield per 60-lb bag. Add 10% when ordering.
| Slab size | Thickness | Cubic feet | Cubic yards | 60-lb bags |
|---|---|---|---|---|
| 8×8 | 4″ | 21.33 | 0.79 | 48 |
| 8×8 | 6″ | 32 | 1.19 | 72 |
| 10×10 | 4″ | 33.33 | 1.23 | 75 |
| 10×10 | 6″ | 50 | 1.85 | 112 |
| 12×12 | 4″ | 48 | 1.78 | 107 |
| 12×12 | 6″ | 72 | 2.67 | 160 |
| 12×16 | 4″ | 64 | 2.37 | 143 |
| 16×16 | 4″ | 85.33 | 3.16 | 190 |
| 20×20 | 4″ | 133.33 | 4.94 | 297 |
| 24×24 | 4″ | 192 | 7.11 | 427 |
Check the yield printed on your product label — most US 60-lb concrete-mix bags state 0.45 ft³, but specialty mixes can differ.
How thick should a 12×12 slab be?
Four inches is the standard for patios, walkways, and shed floors — and it’s what every number on this page assumes. Go thicker (5–6 inches) for driveways or anything carrying vehicles or heavy equipment. Whatever the thickness, the slab should sit on at least 4 inches of compacted gravel sub-base (our gravel calculator handles the sub-base math), and most slabs benefit from reinforcement — wire mesh or rebar on chairs, sized for the load. Our rebar grid calculator estimates bar counts, laps, and weight for a slab grid.
Bags or ready-mix for a 12×12 slab?
A 12×12 slab at 4 inches needs 107–118 sixty-pound bags — roughly 3.21 tons of dry mix to haul, stage, and mix. 107 bags is 3.2 tons of material to haul and mix. Doable with a mixer and a full day, but this is the size where most people switch to ready-mix and never look back. Ready-mix suppliers have minimum-load charges (often 1–3 yards), so call ahead and confirm the short-load fee before you commit.
What does a 12×12 concrete slab cost?
Cost is just your volume times your local price. For bags: 118 bags × the per-bag price at your store. As a rough planning figure, sixty-pound bags commonly run about $4–$6 at US home centers, which puts bag material for this slab in the ballpark of $470–$710 — but treat that as a placeholder and check current shelf prices, which move by region and season. Ready-mix is typically quoted per cubic yard plus delivery, so get two quotes. Forming lumber, gravel sub-base, reinforcement, and labor sit on top of the concrete itself.
Pouring day: what to expect
If you go the bag route, know what you’re signing up for. A typical homeowner-grade 3.5-cubic-foot drum mixer handles about 2 sixty-pound bags per batch — 107 bags means roughly 54 batches. At 10–15 minutes per batch to load, mix, wheel, and place, that’s 9–14 hours of continuous mixing before screeding and finishing even start. Realistically this is a two-person, full-day job — keep the mix consistent batch to batch and don’t start the pour late in the day.
After the pour, protect your work. Concrete is walkable in 24–48 hours, ready for light use in about 7 days, and reaches full design strength around 28 days. Keep it damp for the first few days (a light misting or wet curing cover) and keep vehicles off a new slab for at least a week. Saw-cut control joints within 24 hours — typically one joint every 8–10 feet — to give shrinkage cracks somewhere to go.
How we calculate
Volume uses the rectangular-prism formula (length × width × depth), converted at 27 ft³ per cubic yard. Bag counts divide volume by 0.45 ft³ per 60-lb bag — the yield printed on most US concrete-mix bags; always confirm against your product label. The 10% waste allowance covers uneven excavation, spillage, and minor measurement differences; it is a planning figure, not an engineering specification. Assumes uniform slab thickness over a level, compacted subgrade.
Reviewed September 2026 · TrueMeasure
Frequently asked questions
How many 60-lb bags of concrete do I need for a 12×12 slab?
107 bags at 4 inches thick before waste — 118 with a 10% allowance.
How thick should a 12×12 slab be?
Four inches is standard for patios, walkways, and shed floors; driveways and heavier loads usually call for 5–6 inches. Frost depth, soil conditions, and local code can change the requirement — check before you form up.
Should I order ready-mix or mix bags for a 12×12 slab?
At 1.78 cubic yards, ready-mix usually wins: 107 bags is 3.2 tons to haul and mix. Bags make sense below about one cubic yard.
How much does a 12×12 concrete slab cost?
Materials only, budget roughly $470–$710 for bags (118 × typical $4–$6 per sixty-pound bag) or a per-yard ready-mix quote plus delivery. Forming lumber, gravel sub-base, reinforcement, and labor are on top. Prices vary widely by region — get local quotes.