Concrete Calculator
Cubic yards and bag counts for slabs, footings, and round columns. Waste already handled.
Quick reference: yards for common slabs (4 in thick, 10% waste)
| Slab | Volume | Order | 80 lb bags |
|---|---|---|---|
| 10 x 10 pad | 1.23 yd3 | 1.5 yd3 | 62 |
| 12 x 20 patio | 2.96 yd3 | 3.5 yd3 | 147 |
| 20 x 24 garage | 5.93 yd3 | 6.75 yd3 | 294 |
| 24 x 40 shop | 11.85 yd3 | 13.25 yd3 | 587 |
Anything over about 2 yards, order a truck. Bag mixing past that point costs more in time and money.
Concrete estimating FAQ
How do I calculate cubic yards of concrete?
Length x width in feet x thickness in feet, divided by 27. A 10 x 10 slab at 4 inches is 10 x 10 x 0.333 / 27 = 1.23 cubic yards. Add 5 to 10 percent for waste and uneven subgrade.
How many 80 lb bags of concrete in a yard?
An 80 lb bag yields about 0.60 cubic feet, so one cubic yard (27 cubic feet) takes about 45 bags. A 60 lb bag yields 0.45 cubic feet, about 60 bags per yard.
When should I order a truck instead of bags?
Past about 2 cubic yards (roughly 90 x 80 lb bags), ready mix delivery is cheaper and far faster. Most plants have a 1 yard minimum plus a short load fee under 4 or 5 yards.
How thick should a concrete slab be?
4 inches for patios, sidewalks, and shed pads; 5 to 6 inches for driveways and garage floors that carry vehicles; thicker with rebar for heavy equipment. Check local code and soil conditions.
How much does a yard of concrete cover?
At 4 inches thick, one cubic yard covers 81 square feet. At 6 inches it covers 54 square feet.
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