Concrete for a rectangular, round, L-shaped, or custom patio slab, with bags, gravel base, and how many pavers would cover the same footprint.
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| Item | How it is figured | Quantity |
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This patio concrete calculator figures the slab for the four patio footprints people actually build: a rectangle, a circle, an L-shape made of two rectangles, or any custom area you have already measured. Choose the thickness and a waste allowance and it returns the concrete in cubic feet, cubic yards rounded up to the quarter yard for a ready-mix order, and the number of 40, 60, and 80 lb bags, plus the compacted gravel base underneath. Because many people weigh a poured slab against pavers, the same footprint is also priced as pavers: pick a paver size and the page counts pieces with a 5 percent cutting allowance and sizes the gravel and sand bedding. It is for homeowners planning a backyard patio, comparing concrete with pavers, or checking a contractor's quantities.
Area: rectangle = length x width; circle = pi x (diameter / 2)^2; L-shape = the sum of two rectangles; custom = the area you enter. Concrete volume in cubic feet = area x thickness in inches / 12, multiplied by 1 + waste%, then / 27 for cubic yards and rounded up to the nearest 1/4 yard. Bag counts divide the volume by the standard premix yields of 0.30, 0.45, and 0.60 cubic feet for 40, 60, and 80 lb bags. The gravel base is area x base depth / 12, converted to yards and to tons at 105 lb per cubic foot. The paver alternative divides the area by one paver's face area (width x length / 144) and multiplies by 1.05 for cuts and breakage, with a 4 inch gravel base and a 1 inch sand setting bed figured the same way. Metric mode converts meters and centimeters to feet and inches internally and reports cubic meters and tonnes.
Four inches is standard for a patio that carries people, furniture, and a grill, poured over 4 inches of compacted gravel. Go to 5 or 6 inches under a hot tub, an outdoor kitchen with a masonry pizza oven, or where a vehicle might ever drive across it. Thickness below 3.5 inches cracks easily and makes it hard to keep wire mesh in the middle of the slab. Control joints every 8 to 10 feet keep shrinkage cracks straight.
A 12 x 12 ft patio at 4 inches is 48 cubic feet, or 1.78 cubic yards. That is 160 bags of 40 lb mix, 107 bags of 60 lb, or 80 bags of 80 lb before waste; with 10 percent waste, 176, 118, or 88 bags. At 80 bags you are mixing and hauling more than 6,000 lb by hand, so most people order 2 yards of ready-mix instead, even with the short-load fee.
Poured concrete is usually the lower material cost and the faster install for a plain slab. Pavers cost more per square foot in materials and labor but can be lifted to fix settling, drain through the joints, and never show a shrinkage crack. Enter your local prices for a cubic yard of concrete and for one paver in the cost fields; the calculator counts pieces at your chosen size with 5 percent extra and shows both totals. Base gravel is needed under either choice.
A 4 inch residential patio on a well-compacted base usually uses 6x6 welded wire mesh or synthetic fiber in the mix to hold cracks tight; rebar is not required unless the slab is thicker, spans soft or filled ground, or supports a structure. Whatever you use must sit in the middle of the slab depth, supported on chairs or bricks, not lying on the gravel. Expansion joint material is needed where the slab meets the house foundation.
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