UNDERSTAND THE ANSWER How is this calculated? US inputs use feet for length and width and inches for depth. Metric inputs use meters and centimeters. The result includes the selected waste allowance.
Rectangular concrete volume Volume = Length × Width × Depth × (1 + Waste %)
A practical example A 20 × 12 ft slab that is 4 inches deep has a base volume of about 2.96 cubic yards before waste.
COMMON QUESTIONS Quick answers Why add waste?+ Excavation variation, spillage and uneven subgrade can increase actual material needs. Suppliers can help confirm the final order.
Is ready-mix sold by cubic yard?+ In the US, ready-mix is commonly ordered by cubic yard. Metric suppliers generally use cubic meters.
How many cubic yards of concrete do I need?+ Multiply slab length, width and depth in consistent units, convert cubic feet to cubic yards, then add waste.
How many cubic feet are in a cubic yard?+ One cubic yard contains 27 cubic feet.
How much extra concrete should I order?+ Five to ten percent is common for simple work, but subgrade variation and complex forms may require more.
Can I use this for footings or columns?+ This version models a rectangular slab. Divide complex work into rectangular sections or use a shape-specific estimate.
Should I round the order up?+ Yes. Confirm the supplier’s minimum load and ordering increments before placing the order.