Pre-Calculated Specs for a 20×20 Concrete Slab (5" Depth)
two-car garage floor, heavy vehicular driveway pad, or workshop building foundation80 lb Bags Needed306 bagsincl. 10% waste
Total Volume6.79 yd³183.3 cu ft
Sub-Base Gravel5.68 yd³~307 bags (50 lb)
#4 Rebar Needed~628 ft18" on-center grid
Expert Contractor Recommendation: With 306 bags (~24,480 lbs of concrete), hand-mixing risks exhaustion and dry "cold joints" between batches. Ordering a ready-mix truck delivery is strongly recommended.
Engineering Considerations for 20×20 Pours
A 20×20 slab covers exactly 400 square feet. This size is commonly used for a two-car garage floor, heavy vehicular driveway pad, or workshop building foundation. Because this project requires over 1.8 cubic yards (6.79 cu yds), hand mixing is strongly discouraged due to fatigue and cold joint vulnerability. Coordinate with a local ready-mix dispatch supplier.
| Bag Size | Total Bags Needed | Combined Dry Weight | Estimated Material Cost |
|---|---|---|---|
| 80 lb bag | 306 bags | 24,480 lbs (11,104 kg) | $1775 - $2295 |
| 60 lb bag | 408 bags | 24,480 lbs (11,104 kg) | $1999 - $2611 |
| 50 lb bag | 489 bags | 24,450 lbs (11,090 kg) | $2078 - $2690 |
| 40 lb bag | 612 bags | 24,480 lbs (11,104 kg) | $2203 - $2938 |