Slabs, footings, columns and steps — get cubic yards, cubic meters, and exactly how many bags to buy. Waste factor included.
Multiply length × width × thickness (in feet) to get cubic feet, then divide by 27 for cubic yards. This calculator does the unit conversions for you and adds a waste factor — pros typically order 5–10% extra to cover spillage, uneven subgrade, and over-excavation.
Bag yields: a 40 lb bag yields ≈ 0.30 ft³, a 60 lb bag ≈ 0.45 ft³, and an 80 lb bag ≈ 0.60 ft³ of mixed concrete. For pours over about one cubic yard (≈ 45 × 80 lb bags), ready-mix delivery usually wins on both cost and quality.
Estimates are for planning. Verify thickness and subgrade conditions on site, and check local code for required footing depths and reinforcement.