How Much Concrete for a 4x8 Pad?
Concrete needed
0.43 cubic yards
A 4 by 8 foot pad at four inches, with ten percent on top for waste.
When the figures look right, the concrete material list downloads as a real PDF with your business details on it, built inside your own browser. Nothing you type is uploaded anywhere.
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.
- Length4 ft
- Width8 ft
- Thickness4 in
- Waste allowance10 %
Concrete needed0.43 cubic yards
| Volume | 10.7 cu ft |
|---|---|
| Cubic yards before waste | 0.4 |
| Cubic yards with 10% waste | 0.43order to this number |
| Order in quarter yards | 0.5 cu yd |
| 60 lb bags, if bagging it | 27 |
| 80 lb bags, if bagging it | 20 |
The material list this produces
| Ready mix concrete, cubic yards | 0.5 |
|---|---|
| Rebar or mesh, sq ft of slab | 32 |
| Form lumber, linear ft | 24 |
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 | 0.43 cubic yards |
| 5 in | 0.54 cubic yards |
| 6 in | 0.65 cubic yards |
| 8 in | 0.87 cubic yards |
What else matters here
This is the size of a generator pad, a mini split condenser pad, a small stoop or the landing at the bottom of a set of steps. It is also the last size where mixing it yourself is clearly the right call rather than a stubborn one.
Under a yard, a ready mix supplier will still deliver, but almost all of them charge a short load fee for anything below their minimum, which is commonly one yard and sometimes three. That fee is often more than the concrete, so on a pour this size the question is not what the concrete costs, it is what the trip costs.
Mixing it means the whole pad has to go in wet on wet. Twenty odd bags is roughly an hour of continuous mixing for two people with a mixer, which is fine. Doing it with a wheelbarrow and a hoe is where cold joints come from.
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 many bags of concrete for a 4x8 slab?
Around 27 sixty pound bags or 20 eighty pound bags at four inches thick, including a waste allowance. The exact count is on the page above, and it moves if you change the thickness.
Is a 4x8 pad worth ordering ready mix for?
Usually not on its own. It is under half a yard, and almost every supplier has a minimum load with a short load fee below it. If you have another pour on the same day, add this to that ticket instead.
How thick should an AC or generator pad be?
Four inches is standard for a condenser or a small generator. Go to six if the unit is heavy, if it will be struck by a mower, or if the ground under it is soft.
The concrete calculator takes any dimensions you like and hands back the same list.