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Concrete Pad & Slab Calculator
Use this concrete pad calculator for a slab, patio, shed base or walkway. Get the slab material you need in cubic yards, bag counts and cost in one step.
YOU NEED
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Estimate only. Bag yields, material density and waste vary by product and supplier. Confirm quantities with your supplier and check local building codes before you buy or build.
Concrete needed for common pad sizes
A 10 × 10 ft pad at 4 inches thick takes 1.23 cubic yards before waste. A 12 × 12 ft shed pad takes 1.78, and a 4 × 8 ft walkway section takes 0.40. Enter your own size above to see yards, bags and cost.
Slab thickness by use
Walkways, patios and shed pads are normally 4 inches. Driveways and garage floors are usually 5 to 6 inches, and heavier loads call for thicker concrete and reinforcement. Confirm with your local building department.
Concrete slab material list
A basic slab needs concrete (yards or bags), a compacted gravel base, formwork and reinforcement such as rebar or wire mesh. This calculator covers the concrete; use the gravel calculator for the base under it.
Prepare the base
A 4 inch layer of compacted gravel under the slab drains water and supports the concrete. Calculate that with the gravel calculator and include the extra depth in your formwork.
Frequently asked questions
How much concrete for a 12 x 12 slab?
At 4 inches thick it is 48 cubic feet, 1.78 cubic yards. With 10% waste, about 1.96 cubic yards, or 88 bags of 80 lb.
How many bags of concrete for a 4 x 8 pad?
A 4 × 8 ft pad 4 inches thick is 10.7 cubic feet, about 12 with 10% waste, which is 20 bags of 80 lb or 27 bags of 60 lb.
Does concrete shrink or settle?
A little, and forms rarely hold perfect dimensions. That is why 5 to 10% extra is standard.
How accurate is this estimate?
It is a planning estimate, not an order. Bag yields, material density and waste vary by product, supplier and job, so confirm quantities with your supplier and check local building codes before you buy or pour.
Are my measurements saved?
No. Everything is calculated in your browser. Nothing is uploaded or stored.
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Also on this topic: Concrete calculator, Concrete slab cost calculator.