Over-excavation, spillage and uneven subgrade. 5-10% for formed work, 10-15% on rough ground.
Yields are the figures printed on the bag. Speciality mixes differ — check yours.
Optional. Leave at zero to skip the cost estimate.
Material quantity estimate for planning and purchasing. Not structural engineering advice, not a bid, and not a code determination.
How many yards of concrete for a 20x20 driveway?
A 20 x 20 ft driveway at 5 inches thick needs 6.2 cubic yards of concrete (166.7 cubic feet). Order 6.75 to 7 yards to cover waste and subgrade variation.
At 4 inches it is 4.9 cubic yards, and at 6 inches — the right thickness if a pickup, RV or trailer will park on it — it is 7.4 cubic yards.
This is well past the point where bags make sense: 6.2 cubic yards is about 280 bags at 80 lb. Order ready-mix, specify 3,500-4,000 psi, and ask for air entrainment if you are anywhere that freezes.
Driveway width and thickness
A driveway is one of the few slabs where under-building is expensive rather than merely untidy — a 4 inch pad under a loaded pickup cracks across the wheel path within a couple of winters.
| Layout | Width | Thickness |
|---|---|---|
| Single car | 10-12 ft | 4-5 in |
| Single with walk space | 14 ft | 4-5 in |
| Double car | 20-24 ft | 5 in |
| Pickup / RV / boat | 12+ ft | 6 in |
| Apron at the street | Full width | 6-8 in |
The parts this number does not include
The concrete is usually about half the job. Budget separately for:
- Aggregate base. 4-6 inches of compacted crushed stone. For a 40 x 12 ft drive at 4 inches that is around 6 cubic yards loose, roughly 9 tons.
- Reinforcement. #4 rebar at 16-18 inches on centre each way for a 6 inch slab.
- Mix specification. 3,500-4,000 psi, and air-entrained anywhere that freezes. Air entrainment is a plant order, not something you can add later.
- Jointing. Control joints every 10-12 feet and an isolation joint where the slab meets the garage.
A driveway is almost always past the bag break-even. At 40 x 12 ft and 5 inches you are looking at 200 cubic feet — 7.4 cubic yards, or 333 bags at 80 lb before any waste allowance. Order ready-mix.
Common questions
How many yards of concrete for a 20x20 driveway?
At 5 inches thick, 20 x 20 ft is 166.7 cubic feet, or 6.2 cubic yards. Add 10% for waste and subgrade variation and order 6.75 to 7 yards.
Is 4 inches enough for a driveway?
For passenger cars on a well-compacted base, yes. For anything heavier — a pickup, a trailer, a delivery truck turning around — go to 5 or 6 inches. The extra inch on a 40 x 12 ft drive is about 1.5 cubic yards, far cheaper than replacing a cracked slab.
How long before I can drive on new concrete?
Foot traffic after 24-48 hours, cars after 7 days, heavy vehicles after 28 days. Concrete reaches roughly 70% of design strength in the first week and full strength at 28 days.