Free Concrete Calculator

An 80lb bag of concrete yields approximately 0.60 cubic feet, and a 60lb bag yields around 0.45 cubic feet. This concrete calculator is your go-to tool on how to calculate the amount of concrete required for your project. Whether you're working on a concrete slab, a foundation, or any other concrete structure, our concrete calculator simplifies the process to estimate the volume of concrete needed as well as the number of cement bags needed for your concrete mix. 

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How many bags of concrete do you need per cubic foot?

Usually concrete mix bags are sold in bags of 40lb, 60lb or 80lb.

1 cubic foot requires 3.34 bags (round to 4) of 40lb of concrete mix.

1 cubic foot requires 2.5 bags (round to 3) of 60lb of concrete mix

1 cubic foot requires 1.67 bags (round to 2) of 80lb of concrete mix.

Therefore we can apply the following matrix to calculate the number of bags of concrete needed per volume of slab.

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For example, if you need to build a slab with a volume of 50 ft3, you will need 170 bags of 40lb bags of concrete mix.

You can also use our calculator to assess how much it would cost you if you enter the price for each type of concrete bags at your local supplier. 

How much money do you need to purchase enough concrete to build a slab ?

1x 40lb bag of concrete costs ~ $4.00

1x 60lb bag of concrete costs ~ $5.00

1x 80lb bag of concrete costs ~ $6.00

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Calculating Volume for Round Slabs or Round Columns (cylinder shape):

For round structures like round slabs or columns, you'll use the formula for the volume of a cylinder. Here's how to calculate it:

1. Measure Diameter or Radius: Measure the diameter (the distance across the center) of the round structure, or if you have the radius (half of the diameter), use that measurement. Ensure you use consistent units, such as feet or meters.

2. Measure Depth: Measure the depth or thickness of the concrete you want to pour. This is typically measured in inches or centimeters.

3. Apply the Formula: Use the following formula to calculate the volume in cubic feet or cubic meters:

• If using diameter: Volume (cubic feet or cubic metres) = π x (Diameter/2)^2 x Depth
• If using radius: Volume (cubic feet or cubic metres) = π x Radius^2 x Depth

   Here, π (pi) is approximately 3.1416.

4. How to calculate yards of concrete ? If you prefer to work with cubic yards, you can convert the result by dividing the cubic feet by 27, as 1 cubic yard equals 27 cubic feet.

If you want to convert cubic metres to cubic yards, simply divide cubic metres by 1.308 as 1 cubic metre equals 1.308 cubic yards.

• Volume (cubic yards) = Volume (cubic feet) / 27
• Volume (cubic metres) = Volume (cubic metres) / 1.308

Calculating Volume for Square Slabs, Square Columns, Walls or Footings:

For square or rectangular structures like slabs or columns, you'll use the formula for the volume of a rectangular prism (a box-like shape). Here's how to calculate it:

1. Measure Length and Width: Measure the length and width of the square or rectangular structure in feet or meters. Ensure you use consistent units for both measurements.

2. Measure Depth: Measure the depth or thickness of the concrete you want to pour. This is typically measured in inches or centimeters.

3. Apply the Formula: Multiply the length, width, and depth together to calculate the volume in cubic feet or cubic meters:

• If using feet: Volume (cubic feet) = Length (feet) x Width (feet) x Depth (feet)
• If using meters: Volume (cubic meters) = Length (meters) x Width (meters) x Depth (meters)

4. Convert to Cubic Yards: If you prefer to work with cubic yards, you can convert the result by dividing the cubic feet by 27.

• Volume (cubic yards) = Volume (cubic feet) / 27
• Volume (cubic metres) = Volume (cubic metres) / 1.308

Frequently Asked Questions

How many 80lb bags of concrete do I need for a 10x10 slab?
For a 10x10 slab at 4 inches deep you need approximately 1.23 cubic yards of concrete, which equals roughly 56 bags of 80lb concrete.

How many bags of concrete are in a cubic foot?
One 80lb bag yields approximately 0.60 cubic feet. One 60lb bag yields approximately 0.45 cubic feet.

What is the difference between concrete and cement?
Cement is an ingredient in concrete. Concrete is made by mixing cement, water, sand, and gravel. You cannot use cement alone as a structural material.

How thick should a concrete slab be?
A standard residential slab is 4 inches thick. Driveways are typically 6 inches and high-load areas may require 8 inches or more.

How do I calculate cubic yards of concrete?
Multiply length by width by depth in feet, then divide by 27 to convert cubic feet to cubic yards.

How long does concrete take to cure?
Concrete reaches 70% of its strength within 7 days and full strength at 28 days. Avoid heavy loads for at least 7 days after pouring.