Calculate concrete volume, area, or thickness from two known values, with unit conversions for sq ft, sq m, sq yd, inches, feet, cm, and meters.
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Concrete Volume Formula
The calculator uses the relationship between area, thickness, and volume. The main formula is:
- V = concrete volume
- A = surface area
- T = slab thickness
When using square feet for area and feet for thickness, the result is in cubic feet. If thickness is entered in inches, it is first divided by 12 to convert it to feet.
To calculate concrete volume in cubic feet:
To calculate concrete volume in cubic yards:
To calculate the missing area:
To calculate the missing thickness:
- Volume mode: enter area and thickness to find how much concrete is needed.
- Area mode: enter volume and thickness to find how much surface area that amount of concrete can cover.
- Thickness mode: enter volume and area to find the slab thickness.
Common Concrete Slab Thicknesses
| Project type | Typical thickness | Notes |
|---|---|---|
| Sidewalk | 4 in | Common for foot traffic. |
| Patio | 4 in | May need more thickness for heavy loads. |
| Driveway, passenger vehicles | 4 to 6 in | 6 in is often used for heavier use. |
| Garage slab | 4 to 6 in | Depends on soil, reinforcement, and vehicle weight. |
| Shed slab | 4 in | Typical for small structures on stable base material. |
Concrete Volume Per 100 Square Feet
| Thickness | Cubic feet | Cubic yards |
|---|---|---|
| 3 in | 25.00 ft³ | 0.93 yd³ |
| 4 in | 33.33 ft³ | 1.23 yd³ |
| 5 in | 41.67 ft³ | 1.54 yd³ |
| 6 in | 50.00 ft³ | 1.85 yd³ |
| 8 in | 66.67 ft³ | 2.47 yd³ |
Example Calculations
Example 1: Find concrete volume
You have a 400 square foot slab with a thickness of 4 inches.
The concrete volume needed is about 4.94 cubic yards.
Example 2: Find area
You have 3 cubic yards of concrete and want a 6 inch thick slab.
The concrete can cover 162 square feet at 6 inches thick.
FAQ
Should you add extra concrete to the calculated volume?
Yes, it is common to order slightly more than the exact calculated volume. The calculator gives the geometric volume based on the area and thickness you enter. Real projects can need extra concrete because of uneven subgrade, form variations, spillage, or over-excavation. A common allowance is about 5% to 10% extra, depending on the project.
What is the difference between concrete volume and cement volume?
This calculator estimates concrete volume, not cement volume. Concrete is the finished mixture of cement, sand, aggregate, and water. Cement is only one ingredient in concrete. If you are ordering ready-mix concrete, use the concrete volume result.
Why does thickness need to be converted to feet?
Area in square feet must be multiplied by thickness in feet to produce cubic feet. If thickness is entered in inches, divide by 12 first. For example, 4 inches is 4/12 feet, or 0.3333 feet.
