How much concrete do I need for a 10×20 slab?
A 10 × 20 ft slab poured 4 inches thick needs 2.72 cubic yards of concrete, which is 123 bags of 80 lb mix or 163 bags of 60 lb. That includes 10 percent extra for an uneven base; the exact volume is 2.47 cubic yards (66.7 cubic feet). At 6 inches, for a driveway or garage, it is 4.07 cubic yards or 184 bags of 80 lb.
Concrete for a 10×20 slab by thickness
| Thickness | Exact volume | Order (10% extra) | 80 lb bags | 60 lb bags | 50 lb bags | 40 lb bags |
|---|---|---|---|---|---|---|
| 4 in | 2.47 cu yd (66.7 cu ft) | 2.72 cu yd | 123 | 163 | 196 | 245 |
| 5 in | 3.09 cu yd (83.3 cu ft) | 3.40 cu yd | 153 | 204 | 245 | 306 |
| 6 in | 3.70 cu yd (100.0 cu ft) | 4.07 cu yd | 184 | 245 | 294 | 367 |
Bag counts are rounded up and include the same 10 percent allowance. One 80 lb bag yields 0.60 cubic feet; 60 lb yields 0.45; 50 lb yields 0.375; 40 lb yields 0.30.
Change the numbers
The calculator below is preset for this size. Adjust anything and the results update instantly.
Bags or a ready-mix truck for a 10×20 slab?
This slab sits in the gray zone. Bags are possible (123 of 80 lb, about $800 and 6.2 hours of mixing), but a ready-mix truck delivers 2.72 yards for roughly $340 to $475 plus a short-load fee of $75 to $150, and the whole pour is finished in an hour. Most people go with the truck here; a slab this size poured in batches from bags risks cold joints between batches.
Everything else a 10×20 slab needs
- Gravel base: 4 in of compacted crushed stone over 200 sq ft is 2.72 cubic yards, about 4.1 tons. See the gravel calculator.
- Reinforcement: #4 rebar on a 16 in grid, about 298 linear feet (15 stock bars of 20 ft), or 5 sheets of 5 × 10 ft wire mesh. The rebar calculator prices it out.
- Forms: 60 linear feet of 2 × 4 (9 eight-footers) with a stake every 2 ft, about 30 stakes.
- Vapor barrier: 230 sq ft of 6 mil plastic if the slab is for a shed, garage, or anything enclosed.
- Control joints: cut or tool 1 joint so no panel is longer than 10 ft. Cut within 12 hours of finishing.
- Expansion joint: 1/2 in fiber strip wherever the slab meets a house, driveway, or other concrete.
How the numbers are figured
10 × 20 ft is 200 square feet. Multiply by the thickness in feet (4 in is 0.333 ft) for cubic feet, divide by 27 for cubic yards, and add 10 percent because a gravel base is never perfectly flat. Bag counts divide the cubic feet by each bag's yield. The concrete calculator above does the same math for any size, shape, or waste factor.
Common questions
How many 80 lb bags of concrete for a 10x20 slab?
123 bags at 4 inches thick, 153 bags at 5 inches, or 184 bags at 6 inches, each including 10 percent extra. In 60 lb bags the 4 inch slab takes 163.
How much does concrete for a 10x20 slab cost?
About $800 in 80 lb bags at $6.50 each, or $340 to $475 for 2.72 yards of ready-mix before any short-load fee. Having a contractor form, pour, and finish it typically runs $1,200 to $2,000, or $6 to $10 per square foot.
How thick should a 10x20 concrete slab be?
4 inches for a patio, walkway, shed floor, or hot tub pad on well-compacted gravel. Go to 5 or 6 inches if cars will drive on it, and 6 inches with rebar for a garage, workshop with heavy tools, or RV pad. For a 10×20 slab the jump from 4 to 6 inches adds 1.36 cubic yards.