A 20x20 patio is 400 square feet of outdoor living space, large enough for a dining set, a grill, and comfortable seating. At this scale, the pour is a ready-mix truck delivery, not a bag-mixing project. Attempting 200+ bags of concrete by hand risks cold joints and an exhausting, 6-hour physical ordeal.
At 4 inches thick, a 20x20 patio needs 4.94 cubic yards. With a 10 percent waste buffer, order 5.5 yards. The standard ready-mix truck holds 8 to 10 yards, so your order fits in a single delivery. Schedule the pour for early morning to give yourself the full day for finishing before the concrete sets.
Expansion joints are non-negotiable at this size. Score control joints every 8 to 10 feet in each direction, creating a 2x2 grid of panels. These joints give the concrete a controlled line to crack along during freeze-thaw cycles, keeping your patio surface intact instead of developing random diagonal fractures. Cut joints within 12 hours of pouring using a grooving tool to one-quarter the slab depth.
Finishing transforms a gray slab into an outdoor feature. Broom finish provides slip resistance. Stamped concrete mimics flagstone or brick at $8 to $15 per sqft extra. Exposed aggregate reveals embedded stones for a natural, durable texture at $3 to $6 extra per sqft.
A 20x20 patio at 4 inches thick requires approximately 5.4 cubic yards of concrete with waste factor, delivered by ready-mix truck.
Volume: 20 x 20 x (4/12) = 133.3 cubic feet, divided by 27 = 4.94 cubic yards. Add 10 percent waste for 5.43 yards. Round your order to 5.5 yards to ensure you do not run short mid-pour. A cold joint across a patio is visible for decades.
Use 4,000 PSI concrete for standard foot traffic patios. If you plan to park a vehicle on it occasionally or place a hot tub, specify 4,500 PSI and consider 5-inch thickness. The cost difference between 4,000 and 4,500 PSI is minimal ($5 to $10 per yard) but the strength increase is meaningful.
You need at least 3 people for this pour: one managing the truck chute, one spreading concrete with rakes, and one screeding with a straight board. A fourth person on the float speeds up finishing significantly. The entire pour takes 45 to 90 minutes.
This calculation covers any patio, pool deck section, or outdoor entertainment pad around 400 square feet. If your patio is L-shaped or wraps a corner, calculate each rectangular section separately. For curved edges, approximate with straight segments and add 15 percent extra waste. This is the right calculator for entertaining spaces adjacent to a house, outdoor kitchen pads, and any flat concrete pour between 300 and 600 square feet.