At 4 inches thick, a 20×20 slab has a theoretical volume of about 4.94 cubic yards. Adding 10% waste gives a planning quantity of about 5.43 cubic yards.
Larger pours need better logistics
At this volume, truck access, crew size, placement sequence and finishing time become important planning issues.
Confirm slab design first
Thickness should reflect intended loads, soil, base preparation, reinforcement and local practice.
Ask about delivery charges
Supplier distance, minimums, waiting time and discharge access can change the delivered cost beyond the headline price per yard.
Calculate before scheduling
Use the Concrete Calculator with actual form dimensions and confirm the quantity with the supplier.
Run your own numbers: Model the pour in the Concrete Calculator.