Slab calculator
Concrete Slab Calculator
Calculate concrete for a slab, patio, driveway, sidewalk, or garage floor.
Default slab estimate · length x width x thickness · 40/60/80 lb bags
Slab estimate guide
How to calculate concrete for a slab
Slab formula
For a slab, multiply length by width by thickness to get volume. The calculator converts inches of thickness into feet before calculating cubic feet and cubic yards.
Use this for patios, driveways, sidewalks, garage floors, and other flat rectangular slab work.
slab cubic feet = length x width x thickness
Common slab thickness chart
Thickness depends on the project, subbase, reinforcement, and local requirements. These common values are starting points for material estimating, not structural design.
| Project | Common thickness |
|---|---|
| Patio | 4 inches |
| Sidewalk | 4 inches |
| Driveway | 4-6 inches |
| Garage slab | 4-6 inches |
Example: 10 x 10 slab
A 10 ft by 10 ft slab at 4 inches thick is 33.33 cubic feet before waste. With 10% waste, the estimate is 36.67 cubic feet, or about 1.36 cubic yards.
Using approximate bag yields, that same adjusted volume needs about 123 40 lb bags, 82 60 lb bags, or 62 80 lb bags.
Driveway and patio notes
Driveways and garage slabs are often thicker than patios and sidewalks. If the slab has thickened edges, grade beams, or irregular shapes, estimate those sections separately and add them to the total.
Actual concrete needs may vary based on site conditions, formwork, compaction, and measurement accuracy.
FAQ
Common questions
How thick should a concrete slab be?+
Many patios and sidewalks are about 4 inches thick. Driveways and garage slabs are often 4-6 inches, depending on load, subbase, and local requirements.
How much concrete is needed for a 10 x 10 x 4 inch slab?+
With 10% waste, a 10 ft by 10 ft slab at 4 inches thick needs about 1.36 cubic yards, or about 62 80 lb bags.
Should I order extra concrete for a slab?+
Usually yes. A waste factor helps cover uneven grade, form variation, spills, and small measurement errors.
Does this slab calculator include reinforcement?+
No. It estimates concrete material volume and bags. Rebar, wire mesh, base rock, labor, and finishing are separate items.
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