How Much Concrete for a 10x20 Slab?
Concrete needed
2.72 cubic yards
A 10 by 20 foot slab at four inches, with ten percent on top for waste.
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How that number is worked out
These are the figures this page was built with and every line the calculator produces from them. Change anything above and all of it moves.
- Length10 ft
- Width20 ft
- Thickness4 in
- Waste allowance10 %
Concrete needed2.72 cubic yards
| Volume | 66.7 cu ft |
|---|---|
| Cubic yards before waste | 2.47 |
| Cubic yards with 10% waste | 2.72order to this number |
| Order in quarter yards | 2.75 cu yd |
| 60 lb bags, if bagging it | 163 |
| 80 lb bags, if bagging it | 123 |
The material list this produces
| Ready mix concrete, cubic yards | 2.75 |
|---|---|
| Rebar or mesh, sq ft of slab | 200 |
| Form lumber, linear ft | 60 |
Thickness compared
Thickness is the one number on this page worth arguing about, so here is the same slab at each of the usual four.
| Thickness | Concrete needed |
|---|---|
| 4 in | 2.72 cubic yards |
| 5 in | 3.4 cubic yards |
| 6 in | 4.07 cubic yards |
| 8 in | 5.43 cubic yards |
What else matters here
Ten by twenty is a single car parking pad or a driveway apron, and at just under three yards it is a straightforward truck pour that two people can place and finish.
Slope it. A flat parking slab holds water, and water that sits on concrete through a freeze and thaw cycle is what lifts the surface off in flakes. A quarter inch of fall per foot away from any building is the normal figure, which across ten feet is two and a half inches.
Twenty feet needs joints at roughly ten foot spacing, so two joints across the width, giving three panels around 10 by 6.7. That is close enough to square to behave. Running the joints the other way, along the length, would give three long thin strips that crack across the middle of each.
What this calculator assumes
- One cubic yard is 27 cubic feet. A 4 inch slab is one third of a foot thick, not 4.
- A 60 lb bag yields about 0.45 cubic feet and an 80 lb bag about 0.60. Bags are for small pours only; past about one cubic yard, ready mix is cheaper and far less work.
- Ready mix is usually sold in quarter yard steps with a short load fee below one yard.
Questions people ask
How much concrete for a 10x20 slab?
About 2.72 cubic yards at 4 inches with waste, so order 2.75 or 3 yards.
How much slope does a parking pad need?
Around a quarter inch per foot away from any building, so two and a half inches of fall across a ten foot pad. Flat slabs hold water and spall in freeze and thaw.
Is 4 inches enough for a car?
For cars and light vehicles on a well compacted base, yes. Trucks, RVs and anything regularly loaded want six inches.
The concrete calculator takes any dimensions you like and hands back the same list.