Pick a slab size for the concrete you need in cubic yards or cubic metres and the number of bags. Every page shows the formula and the other unit system. For a size not listed, use the interactive concrete calculator.
Imperial slab sizes (feet)
8x8 at 4 in
10x10 at 4 in
10x12 at 4 in
12x12 at 4 in
12x16 at 4 in
12x20 at 4 in
15x15 at 4 in
16x16 at 4 in
16x20 at 4 in
20x20 at 4 in
10x20 at 4 in
12x24 at 4 in
20x24 at 4 in
24x24 at 4 in
20x30 at 4 in
24x36 at 4 in
30x30 at 4 in
40x40 at 4 in
20x20 at 6 in
24x24 at 6 in
20x30 at 6 in
24x36 at 6 in
30x30 at 6 in
12x20 at 6 in
12x24 at 6 in
10x20 at 6 in
Metric slab sizes (metres)
Mixing more than a few bags? A heavy duty mixing tub keeps the batch consistent and saves your back. For larger pours, price up ready mix delivery instead.
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Common questions
How do I work out concrete for any slab?
Multiply length by width by thickness for the volume, then divide by 27 for cubic yards. Add waste and round up to whole bags. Use the interactive calculator for any size.
What thickness should a slab be?
Four inches (about 10 cm) suits patios and walkways. Driveways and garage floors are usually 5 to 6 inches (13 to 15 cm). Check local requirements for structural work.
More Calculators
Concrete New
Enter slab dimensions. Result rounds up with a 7 percent waste allowance.
Gravel New
Enter the area dimensions and depth. Result rounds up with a 5 percent waste allowance.
Mulch New
Enter the bed area and depth. Result rounds up with a 5 percent allowance.
Topsoil New
Enter the area and depth. Result rounds up with a 5 percent allowance.
Paint New
Enter total wall area and coats. Result rounds up to whole units.
Flooring New
Enter room area and the coverage printed on the box. 10 percent waste added.
Tile New
Enter the area and one tile size. 10 percent waste added.
Drywall New
Enter total area to cover. 10 percent waste added.
Paver New
Enter the patio size and one paver size. 5 percent waste added.
Sand New
Enter the area and depth. 5 percent allowance added.
Roofing New
Enter the roof surface area. 10 percent waste added. Three bundles per square.
Insulation New
Enter area to cover and the coverage printed on the package. 5 percent added.
Fence New
Enter total fence length and post spacing.
Sod New
Enter the area to cover. 5 percent allowance added.
Grass Seed New
Enter area and seeding rate. Default rates suit a new lawn.
Fertilizer New
Enter area, target nitrogen rate and the first number on the bag.
Cubic Yards New
Enter length, width and depth. No waste added.
Square Footage New
Enter length and width.
Board Foot New
Enter board dimensions and quantity.
Material Cost New
Enter quantity, unit price, tax and delivery. Figures are in your own currency.