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How to Calculate Rebar for Your Project

If you are here, there is a good chance that you are planning a build. This could be for a project you are building yourself or one that you are having done. Either way, it is a good idea to get the right amount of rebar and to understand how this is calculated. The more you know the better for you and your budget. So let’s jump into some details and how to calculate rebar for your project.

What is Rebar?

Rebar is a reinforcing steel bar that is made with hot-rolled bars with a deformed surface. They are very long rods that can be bent or cut to the needed size or shape. Standard rebar codes exist for bending called a bending schedule, you can read more about it: What is a bar bending schedule?.

Where is Rebar Used?

Rebar is most often used in concrete construction. The rebar looks like long steel rods with ribs on them for better adhesion with the concrete. The reinforcing bars are linked together and bent into shape for the foundations, pillars, and upstairs floors. Though rebar can be used in many other applications. Concrete itself has a low tensile strength, meaning that it does not do well with a twisting force. Rebar is placed inside the concrete while it is still wet. The concrete dries and adheres to the rebar. The rebar adds that much-needed tensile strength for a structural sound building. Ultimately reducing any cracks that may occur and improving its load bearing ability.

What is the Rebar Calculation?

Things can get a little tricky when you need to calculate the rebar needed for your project. The foundation or driveway is typically a flat grid, so it may be easiest to start there and then look at more complicated elements when beginning with the calculation.

Slab Size
Where you are pouring the concrete will be your slab. The rebar needs to sit within the slab and away from the edge of the slab. Effectively creating a border all around the rebar grid. So you will want to take note of the slab length and width. Then determine the space needed between the rebar and slab edge. All of these measurements are vital to properly calculating the rebar for the projects.

Let’s say that the slab is 600 cm (length) x 400 cm (width) with an edge clearance of 8 cm.

Rebar-Rebar Spacing
The first thing to consider is what the rebar-rebar spacing will be. Rebar is most often laid out in a grid formation. However, the rebar and spacing used is different for each project. Find out what is best suited for your needs from your rebar supplier.

To continue our example let’s assume that the spacing between the rebar is 40 cm.

Rebar Grid Dimensions
Now that you know the clearance to the slab edge, rebar-rebar spacing and the slab size, you can work out the rebar grid dimensions.
Grid Length
The calculation for the grid length is:

Grid length = slab length – (2x slab edge clearance)

600 – (2×8) = 584 cm
Grid Width
The calculation for the grid width is:

Grid width = slab width – (2x slab edge clearance)

400 – (2×8) = 384 cm

Now we know that for our example, the grid dimensions for the rebar will be 584 cm x 384 cm

Total Rebar Length
To work out the total rebar length we need to calculate the number of rows and columns for the project. Here is the calculation for each:

Rows: grid length ÷ rebar-rebar spacing
Columns: grid width ÷ rebar-rebar spacing

For our example:

Rows: 584 ÷ 40 = 14.6
Columns: 384 ÷ 40 = 9.6

Now to calculate the total rebar length needed, we have all the measurements. The formula to get the total length is:

Total rebar length = (rebar columns x rebar length) + (rebar rows x rebar width)

(9.6 x 584) + (14.6 x 384) = 11212.8 cm (112.13 meters)

Rebar Rods

The picture of what is needed is starting to become clearer. With all these calculations one can now work out just how many rebar rods need to be ordered for the project. Let’s assume that your rebar supplier sells them in 6 m pieces (600 cm).

rebar pieces = total rebars length ÷ single rebar length

11212.80 ÷ 600 = 18.69

Since rebar is sold in set pieces you can round up the number. In this case it means that 19 rods are required for the project.

Get Started

Unfortunately it is not always entirely easy to calculate the rebar or your project. At least for simple projects these calculations will assist, and even give you a bit more clarity on how it is decided how much rebar is needed for your project.

But now that you have an idea of what you need, you can go ahead and talk to your rebar supplier or architect to begin your project. If you are still in the market for a supplier, consider contacting us for more details on our rebar products. We are leaders in the field and take pride in formulating the best solution for you.