Concrete calculator: cubic yards, bags and cost
Work out how much concrete a slab, footing, wall or round column needs. Enter the dimensions and how many there are, and get the cubic yards to order with waste, the number of premix bags if the pour is small, the truckloads if it is not, and the cost at your supplier’s price.
Concrete: cubic yards, bags & truckloads
Slab, footing, wall or round column: enter the dimensions and how many there are, and get the volume with waste, the number of premix bags, the truckloads, and the cost at your price per yard.
The pour
Result
Volume (ft³) = length × width × thickness ÷ 12, or π × (diameter ÷ 24)² × height for a column, × how many. Cubic yards = ft³ ÷ 27, then × (1 + waste %). Bags: an 80 lb bag of premix yields about 0.60 ft³, a 60 lb bag 0.45 ft³ and a 40 lb bag 0.30 ft³. Truckloads assume 10 yd³ per truck. Check bag yields on the bag you buy.
How to use it
- Choose the shape: rectangular (slab, footing, wall) or a round column.
- Enter length and width in feet and thickness in inches — or the column’s diameter and height.
- Enter how many identical pours there are, and a waste allowance (5–10% is common).
- Enter your ready-mix price per cubic yard, and read the yards, bags, trucks and cost.
A worked example
Questions
How do you calculate cubic yards of concrete?
Multiply length × width in feet by thickness in inches ÷ 12 to get cubic feet, then divide by 27. A 10 × 10 ft slab at 4 in is 33.3 ft³, or 1.23 cubic yards.
How many 80 lb bags of concrete make a yard?
About 45. An 80 lb bag of premix yields roughly 0.6 ft³ and a cubic yard is 27 ft³. A 60 lb bag yields about 0.45 ft³, so 60 bags make a yard.
How much extra concrete should I order?
Most contractors add 5–10% for spillage, form deflection and an uneven subgrade, then round up to the supplier’s ordering increment. Running short mid-pour costs far more than a quarter yard left over.
How many yards of concrete are in a truck?
A typical ready-mix truck carries 8–10 cubic yards, and some carry up to 11. Smaller loads usually carry a short-load fee, so ask your supplier for the minimum.
How thick should a concrete slab be?
Four inches is common for patios, walks and garage floors; driveways and slabs carrying heavier loads are often 5–6 inches. The drawings or your local code govern — this calculator only does the quantities.
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