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Concrete for a 12x12 Slab
A 12 × 12 ft slab at 4 inches thick needs about 1.96 cubic yards of concrete including 10% waste. Change the thickness or bag size below for your own job.
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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.
How much concrete for a 12x12 slab?
A 12 × 12 ft slab covers 144 square feet. At 4 inches thick that is 48 cubic feet, or 1.78 cubic yards before waste. Add 10% for spillage and uneven ground and order about 1.96 cubic yards (1.5 m³).
Bags of concrete for a 12x12 slab
With 10% waste, a 4 inch 12x12 slab takes 88 bags of 80 lb mix, 118 bags of 60 lb or 176 bags of 40 lb. Above about one cubic yard, ready-mix delivery is usually cheaper and much faster than mixing bags by hand.
12x12 slab at 5 or 6 inches thick
Driveways, garage floors and slabs for heavy loads are usually 5 to 6 inches. At 6 inches the same 12x12 slab needs 2.93 cubic yards with waste, which weighs about 5.9 US tons wet. Check local building codes for your use.
Don't forget the base
Most slabs sit on 4 inches of compacted gravel. For 12x12 that is about 3.5 US tons of crushed base with waste and compaction. Use the gravel calculator to change the depth or material.
Frequently asked questions
How many yards of concrete for a 12x12 slab?
1.78 cubic yards at 4 inches thick before waste, about 1.96 with 10% extra. At 6 inches it is about 2.93 with waste.
How many 80 lb bags of concrete for a 12x12 slab?
About 88 bags at 4 inches thick, including 10% waste. Each 80 lb bag yields about 0.6 cubic feet.
How much does a 12x12 concrete slab weigh?
At 4 inches thick with waste, about 7,920 lb (4 US tons) of wet concrete, at 150 lb per cubic foot.
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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Common sizes: 10x10 slab, 10x20 slab, 12x20 slab, 16x20 slab, 20x20 slab, 20x30 slab, 24x24 slab, 30x30 slab, 30x40 slab.