Concrete Slab Calculator
Calculate the amount of concrete needed for your slab project. Enter the slab dimensions to estimate the concrete volume and the number of cubic yards required.
Concrete Slab Calculator
Estimate the concrete needed for your slab. Enter your slab area, choose the thickness, and get the total volume in cubic yards, cubic feet, and cubic meters.
Your Concrete Estimate
Calculated from your slab dimensions and selected thickness.
Compare Different Slab Thicknesses
| Thickness | Concrete Needed |
|---|
A concrete slab may look simple, but getting the concrete quantity right starts with three measurements: length, width, and thickness.
Use the calculator above to find the volume of concrete required for a rectangular slab. Enter your dimensions in feet and inches or metric units, and the result will show how much concrete you need in the selected volume unit.
The calculation can be useful when planning a new slab, checking a contractor’s estimate, or working out how much ready-mix concrete to order.
Concrete Slab Calculation at a Glance
For a rectangular slab, the calculation is straightforward:
Concrete volume = Length × Width × Thickness
The important part is making sure all three measurements are expressed in compatible units before calculating.
If you are working in feet and inches and want the answer in cubic yards:
Cubic yards = Length × Width × Thickness ÷ 324
Here, length and width are measured in feet, while thickness is measured in inches.
Example
Suppose your slab is:
- Length: 24 feet
- Width: 12 feet
- Thickness: 4 inches
The calculation is:
24 × 12 × 4 ÷ 324 = 3.56 cubic yards
So the slab contains approximately 3.56 cubic yards of concrete before allowing for extra material.
How Much Concrete Does Your Slab Need?
The size of the slab is only part of the calculation. Thickness makes a major difference.
Consider a 20 × 20 foot slab:
| Slab thickness | Approx. concrete |
|---|---|
| 3 inches | 3.70 cubic yards |
| 4 inches | 4.94 cubic yards |
| 5 inches | 6.17 cubic yards |
| 6 inches | 7.41 cubic yards |
| 8 inches | 9.88 cubic yards |
These figures represent the calculated slab volume without an additional waste allowance.
This is why entering the actual planned thickness is important rather than using a standard thickness automatically.
What Measurements Do You Need?
You only need three dimensions for a basic rectangular slab.
Length
Measure from one end of the slab to the other.
Width
Measure across the slab at a right angle to the length.
Thickness
Measure the depth of the concrete slab.
If the slab has different thicknesses in different areas, a single calculation may not accurately represent the entire project. In that situation, calculate the individual sections separately.
A Quick Way to Estimate Concrete
If you already know the slab’s area in square feet, you can make the calculation even quicker.
For a 4-inch-thick slab, every square foot requires approximately:
0.01235 cubic yards of concrete
So:
Slab area × 0.01235 = cubic yards
For example, a 500-square-foot slab at 4 inches thick:
500 × 0.01235 = 6.17 cubic yards
This is the theoretical volume before adding extra concrete.