How this calculator works
This runs our concrete, gravel and rebar calculators on one set of measurements. The slab volume is the area times the thickness, with your waste allowance; the gravel base is the area times the base depth with 20% extra because loose stone compacts; the rebar is a grid at 18 inch centers; and the forms and stakes come from the perimeter. Control joints are placed so that no panel is longer than the spacing you choose in either direction.
Worked example: a 20 × 12 ft driveway (240 ft²) poured 5 inches thick needs 4.07 cubic yards with 10% extra (3.70 without), which is 1 truck load, on about 7.5 tons of crushed stone for a 6 inch base. It takes 18 twenty-foot lengths of #4 rebar, 8 form boards with 26 stakes, and 32 ft of control joints. At 4 inches thick it needs 3.26 cubic yards, and at 6 inches 4.89. A 40 × 20 ft double drive needs 13.6 cubic yards.
Concrete for common driveways (5 in slab, 10% waste)
Cubic yards, truck loads and bags of 80 lb mix.
| Driveway | Area | Concrete | Truck loads | Base stone |
|---|---|---|---|---|
| 20 × 10 ft | 200 ft² | 3.4 yd³ | 1 | 6.2 tons |
| 20 × 12 ft | 240 ft² | 4.1 yd³ | 1 | 7.5 tons |
| 24 × 12 ft | 288 ft² | 4.9 yd³ | 1 | 9.0 tons |
| 40 × 12 ft | 480 ft² | 8.1 yd³ | 1 | 14.9 tons |
| 30 × 20 ft | 600 ft² | 10.2 yd³ | 2 | 18.7 tons |
| 50 × 20 ft | 1000 ft² | 17.0 yd³ | 2 | 31.1 tons |
Tips before you buy
- Most plants have a minimum load of about 3 or 4 cubic yards. If your drive needs less, ask for the short-load charge, or pour in two sections.
- Compact the base in layers with a plate compactor, and slope the drive at least 1/4 inch per foot (2%) so water runs off.
- Cut or tool control joints within 6 to 12 hours of finishing, so that cracks follow the joints. The depth is a quarter of the slab thickness.
- Do not pour in heavy rain or when it may freeze within a few days, and keep the slab damp or covered for about a week.
- Check the rules where the drive meets the street: the apron usually has to meet the public thickness and often needs a permit.
Tools & materials for this project
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Frequently asked questions
How much concrete do I need for a 20x12 driveway?
A 20 × 12 ft driveway 5 inches thick needs 3.70 cubic yards before waste and 4.07 cubic yards with 10% extra. At 4 inches thick it is 3.26, and at 6 inches 4.89.
How thick should a concrete driveway be?
At least 4 inches for cars, 5 inches for cars and light trucks, and 6 inches if heavy trucks or an RV will use it. Each extra inch on a 20 × 12 ft drive adds about 0.81 cubic yards.
How much gravel base does a concrete driveway need?
Four to eight inches of compacted crushed stone, depending on the soil. A 6 inch base for a 20 × 12 ft drive takes about 7.5 tons, with 20% extra for compaction.
Does a concrete driveway need rebar?
Reinforcement does not stop concrete cracking, but it holds the cracks tight. A #4 grid at 18 inch centers takes 18 bars of 20 ft for a 20 × 12 ft drive, or 5 sheets of wire mesh. Your code may require it.
How far apart should control joints be?
Roughly two to three times the slab thickness in feet: 10 feet for a 5 inch slab. That makes 32 ft of joints for a 20 × 12 ft drive.
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Related calculators & guides
Estimates only. Results assume standard materials and simple shapes. Supplier products vary, and the final call on quantity, structure and safety is yours. Check your local code and your supplier's guidance before ordering.