Slab size chart
How much concrete for a slab?
A 10×10 ft slab at 4 inches thick needs 1.23 cubic yards of concrete, and a 12×12 needs 1.78. The charts below cover the most common slab sizes at 4, 5 and 6 inches thick, with bag counts for each.
By the EstimateCement team ·
4-inch slabs
Concrete for a 4″ slab.
Typical for: Patios, walkways, shed floors and hot tub pads.
| Slab (4″ thick) | Cubic yards | Order (+10%) | 60 lb bags | 80 lb bags |
|---|---|---|---|---|
| 4 × 4 ft | 0.20 yd³ | 0.22 yd³ | 14 | 10 |
| 8 × 8 ft | 0.79 yd³ | 0.87 yd³ | 53 | 40 |
| 10 × 10 ft | 1.23 yd³ | 1.36 yd³ | 82 | 62 |
| 10 × 12 ft | 1.48 yd³ | 1.63 yd³ | 98 | 74 |
| 12 × 12 ft | 1.78 yd³ | 1.96 yd³ | 118 | 88 |
| 10 × 20 ft | 2.47 yd³ | 2.72 yd³ | 163 | 123 |
| 12 × 20 ft | 2.96 yd³ | 3.26 yd³ | 196 | 147 |
| 16 × 16 ft | 3.16 yd³ | 3.48 yd³ | 209 | 157 |
| 20 × 20 ft | 4.94 yd³ | 5.43 yd³ | 326 | 245 |
| 24 × 24 ft | 7.11 yd³ | 7.82 yd³ | 470 | 352 |
Bag counts include 10% waste and round up to whole bags.
5-inch slabs
Concrete for a 5″ slab.
Typical for: Driveways for cars, garage floors.
| Slab (5″ thick) | Cubic yards | Order (+10%) | 60 lb bags | 80 lb bags |
|---|---|---|---|---|
| 4 × 4 ft | 0.25 yd³ | 0.27 yd³ | 17 | 13 |
| 8 × 8 ft | 0.99 yd³ | 1.09 yd³ | 66 | 49 |
| 10 × 10 ft | 1.54 yd³ | 1.70 yd³ | 102 | 77 |
| 10 × 12 ft | 1.85 yd³ | 2.04 yd³ | 123 | 92 |
| 12 × 12 ft | 2.22 yd³ | 2.44 yd³ | 147 | 110 |
| 10 × 20 ft | 3.09 yd³ | 3.40 yd³ | 204 | 153 |
| 12 × 20 ft | 3.70 yd³ | 4.07 yd³ | 245 | 184 |
| 16 × 16 ft | 3.95 yd³ | 4.35 yd³ | 261 | 196 |
| 20 × 20 ft | 6.17 yd³ | 6.79 yd³ | 408 | 306 |
| 24 × 24 ft | 8.89 yd³ | 9.78 yd³ | 587 | 440 |
Bag counts include 10% waste and round up to whole bags.
6-inch slabs
Concrete for a 6″ slab.
Typical for: Driveways for trucks or RVs, heavier equipment pads.
| Slab (6″ thick) | Cubic yards | Order (+10%) | 60 lb bags | 80 lb bags |
|---|---|---|---|---|
| 4 × 4 ft | 0.30 yd³ | 0.33 yd³ | 20 | 15 |
| 8 × 8 ft | 1.19 yd³ | 1.30 yd³ | 79 | 59 |
| 10 × 10 ft | 1.85 yd³ | 2.04 yd³ | 123 | 92 |
| 10 × 12 ft | 2.22 yd³ | 2.44 yd³ | 147 | 110 |
| 12 × 12 ft | 2.67 yd³ | 2.93 yd³ | 176 | 132 |
| 10 × 20 ft | 3.70 yd³ | 4.07 yd³ | 245 | 184 |
| 12 × 20 ft | 4.44 yd³ | 4.89 yd³ | 294 | 220 |
| 16 × 16 ft | 4.74 yd³ | 5.21 yd³ | 313 | 235 |
| 20 × 20 ft | 7.41 yd³ | 8.15 yd³ | 489 | 367 |
| 24 × 24 ft | 10.67 yd³ | 11.73 yd³ | 704 | 528 |
Bag counts include 10% waste and round up to whole bags.
Your size isn't listed?
Length × width × thickness ÷ 324.
With length and width in feet and thickness in inches, multiply the three and divide by 324 to get cubic yards. (324 is 27 cubic feet per yard × 12 inches per foot.) For a 14 × 18 ft slab at 4 inches: 14 × 18 × 4 ÷ 324 = 3.11 yd³.
Or skip the math: the slab calculator takes any size and adds waste, bag counts, a gravel base and cost.
Before you order
Three things that change the number.
- Uneven sub-grade. A low spot of just half an inch across a 12×12 slab adds about 0.2 yd³. Grade and compact first, then measure depth in several places.
- Thickened edges. Slabs for sheds and garages often have a deeper perimeter. Estimate the edge as a separate footing and add it.
- Running short costs more than leftovers. A second truck or a cold joint is worse than a little extra concrete, so keep the 10% waste allowance.
FAQ
Common questions
How much concrete do I need for a 10×10 slab?
At 4 inches thick, a 10×10 ft slab is 1.23 cubic yards. With 10% waste, order 1.36 yd³, or 62 bags of 80 lb mix.
How much concrete do I need for a 12×12 slab?
At 4 inches thick, 1.78 cubic yards. With 10% waste, order 1.96 yd³ (most suppliers round to 2 yards), or 88 bags of 80 lb mix.
How much concrete do I need for a 20×20 slab?
At 4 inches thick, 4.94 cubic yards, or 5.43 yd³ with 10% waste. At that size, ready-mix delivery is far cheaper and faster than 245 bags.
How much concrete for a 24×24 garage floor?
At 5 inches thick, a common garage-floor thickness, 8.89 cubic yards. Order 9.78 yd³ with 10% waste.
How many square feet does a yard of concrete cover?
81 sq ft at 4 inches thick, about 65 sq ft at 5 inches, and 54 sq ft at 6 inches. Divide 324 by the thickness in inches to get square feet per cubic yard.
Work it out for your project