Formula
How this estimate works
cubic yards = cubic feet / 27
A 30 ft by 12 ft slab at 5 in thick with 10% waste needs about 6.11 cubic yards.
Why concrete is ordered by cubic yard
Ready-mix concrete is usually ordered by volume. After calculating cubic feet, divide by 27 because one cubic yard contains 27 cubic feet.
Rounding cubic yards
Suppliers may have minimum orders or rounding rules. Use the calculator result as a planning number, then confirm ordering increments locally.
Assumptions used
- Normal-weight concrete is estimated at 150 lb per cubic foot.
- Premix bag yield is estimated from common 40, 50, 60, and 80 lb bag sizes.
- Waste factor is applied after the base volume is calculated.
Before you order materials
- Ask suppliers about minimum orders and rounding increments.
- Include waste before placing an order.
- Confirm access, delivery timing, and placement method.
Frequently asked questions
How do I convert cubic feet to cubic yards?
Divide cubic feet by 27 because one cubic yard contains 27 cubic feet. This is the standard conversion used for ready-mix planning.
Should I round up cubic yards?
Usually yes. Running short during a pour is costly, so many projects include 5% to 10% extra.
Does this work for walls and footings?
Yes. Select the matching shape and enter the relevant dimensions.