How Much Concrete for a 30x30 Slab?
Concrete needed
12.22 cubic yards
A 30 by 30 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.
- Length30 ft
- Width30 ft
- Thickness4 in
- Waste allowance10 %
Concrete needed12.22 cubic yards
| Volume | 300 cu ft |
|---|---|
| Cubic yards before waste | 11.11 |
| Cubic yards with 10% waste | 12.22order to this number |
| Order in quarter yards | 12.25 cu yd |
| 60 lb bags, if bagging it | 734 |
| 80 lb bags, if bagging it | 550 |
The material list this produces
| Ready mix concrete, cubic yards | 12.25 |
|---|---|
| Rebar or mesh, sq ft of slab | 900 |
| Form lumber, linear ft | 120 |
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 | 12.22 cubic yards |
| 5 in | 15.28 cubic yards |
| 6 in | 18.33 cubic yards |
| 8 in | 24.44 cubic yards |
What else matters here
Nine hundred square feet and twelve and a quarter yards, which is more than most ready mix trucks carry. Typical drum capacity is eight to ten yards, so this is two loads, and two loads means the second truck has to arrive while the first pour is still workable.
That scheduling is the job. Trucks are dispatched, not summoned, and a second load that turns up forty minutes late leaves a cold joint across a shop floor. Book both loads together, tell the dispatcher it is a continuous pour, and have the placing crew sized so the first load is down and screeded before the second arrives.
At four inches this is a shop or barn floor for foot traffic and light storage. Anything with a vehicle lift, a press or stacked material wants six inches minimum and a properly engineered base, and at that point it is worth having the thickness specified by somebody who has seen the loads rather than taken from a table.
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 30x30 slab?
About 12.22 cubic yards at 4 inches with waste, which is two ready mix loads for most suppliers.
How many yards does a concrete truck hold?
Commonly eight to ten. A 30 by 30 slab at four inches needs two loads, booked together as a continuous pour.
How thick should a shop floor be?
Four inches for foot traffic and light storage. Six inches minimum for vehicles, lifts or stacked material, over a base built for the load.
The concrete calculator takes any dimensions you like and hands back the same list.