Concrete Calculator
Calculate concrete volume and bags needed for any project
Cubic Yards
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Frequently Asked Questions
How many bags of concrete per cubic yard?
At 60 lb bags: approximately 60 bags per cubic yard (1 bag = 0.45 cu ft, 1 cu yd = 27 cu ft, 27/0.45 = 60). At 80 lb bags: approximately 45 bags per cubic yard. Always add 10% extra for waste and overfill. Mix coverage can vary slightly by brand.
How thick should a concrete slab be?
Sidewalk/patio: 4 inches. Residential driveway: 4-6 inches. Garage floor: 4-6 inches. Road pavement: 6-8 inches. Heavy industrial: 8+ inches. Footings extend below the frost line (varies by climate). Always check local building codes.
What is the correct concrete mix ratio?
Standard mix (3000 psi): 1 part cement: 2 parts sand: 3 parts gravel (1:2:3) by volume, plus water-cement ratio of 0.5-0.6. For bags: follow manufacturer instructions — typically 2.5 quarts of water per 60 lb bag for 80% strength. Too much water weakens concrete.
How long does concrete take to cure?
Concrete reaches initial set in 24-48 hours (do not walk on). 70% strength in 7 days. Full strength (28-day strength) in 28 days. Avoid freezing temperatures in first 24-48 hours. Keep moist for 7 days by covering with wet burlap or plastic sheeting for optimal curing.
When should I use ready-mix vs bagged concrete?
Bagged concrete (60/80 lb bags): small projects under 1 cubic yard — patching, fence posts, small slabs. Ready-mix truck: over 1 cubic yard, large slabs, driveways, foundations. Ready-mix is usually more cost-effective above 0.5 cubic yards and gives better quality control.
Concrete Slab Examples
| Slab Size | 4in thick | 60lb bags |
|---|---|---|
| 5 ft × 5 ft | 0.31 yd³ | ~19 |
| 10 ft × 10 ft | 1.23 yd³ | ~74 |
| 12 ft × 12 ft | 1.78 yd³ | ~107 |
| 20 ft × 20 ft | 4.94 yd³ | ~296 |
| 8 ft × 20 ft | 1.98 yd³ | ~119 |