How to Calculate How Much Rebar You Need

How to Calculate How Much Rebar You Need

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When it comes to concrete, something that you need to know all about is rebar. Of course, it is used to strengthen and reinforce concrete, with one of the main applications being to make large concrete buildings more resistant to earthquakes, as well as to make foundations better able to bear large quantities of weight.

There are indeed many benefits that inserting rebar into concrete brings to the table. With that being said, not only is adding rebar into concrete important but how much of it you use makes a difference too.

How to Calculate the Amount of Rebar You Need

Alright, so the main thing that we’re here to figure out today is how to calculate the amount of rebar you need to put into your concrete. Although this may sound quite intimidating, the fact of the matter is that the calculation only involves a few fairly simple steps.

Although we are about to tell you how to calculate how much rebar you need in a step-by-step manner, do keep in mind that there are many online rebar calculators, where all you need to do is to insert the required parameters, and all of the heavy calculating gets done for you. That aside, let’s figure out how to manually calculate how much rebar you need.

Keep in mind that if you are constructing a building, you will need to determine how much rebar you need for both the foundation and the walls, so our step-by-step tutorial is going to include both of those.

Step 1: Calculating the Linear Feet of the Foundation

The first step in this process is to determine the linear feet of your foundation, or in other words, the size of it. For example, if your foundation is to be 20 feet long and 40 feet wide, the calculation would be 20 + 20 + 40 + 40 = 120 linear feet.

This is a very important step, and everything you do afterward will depend on this step, the linear feet, being properly calculated. Once you have figured out the linear footage of the foundation, you can then move onto step number two.

Step 2: Determine the Amount of Rebar Required for the Footings

What you need to do now is to figure out how much rebar you will need for the footing of your foundations. Keep in mind that the footing is the base of your foundation, so this is of course very important.

Another thing to keep in mind here is that the general rule of thumb is that you need one piece of rebar for every eight inches of footing. Therefore, if the footing is 32 inches, you will require four pieces of rebar, and so on and so forth.

For another example, if your footings have a total length of 140 feet, and they are each 32 inches wide (32 inches requires four pieces of rebar), you would multiply 140 x 4, which equals 560. Rebar generally comes in 20-foot pieces, so you would divide 460 by 20, which therefore means that you need 23 pieces of 20-foot rebar.

Step 3: Determine the Amount of Rebar Required for the Foundation Walls

The next thing that you need to consider is that every four feet of the foundation wall will require concrete and rebar. So, if you have a foundation wall that is 140 feet in total, you would divide that by four, to get a total of 35, which is the number of block cells that will need to be filled with rebar and concrete.

Now, if your foundation is 32 inches, this means that you need to multiply those 32 inches by the 35 slots, which equals 1,120 inches. You need this measurement to be in feet, so divide 1,120 by 12, which equals 93.3 feet of rebar. Remember that you will also need five pieces of 20-foot rebar for the vertical runs.

Step 4: Adding Step-Up Rebar

All you need to do now is to add the total of step-up rebar you will need in order to attach together at the step-ups of the footings. There you have it folks, how to calculate exactly how much rebar you will need.

What Happens If You Put Too Much or Too Little Rebar into Concrete?

What is also important to note when it comes to putting rebar in concrete is that there is such a thing as too much or too little. Now, too much rebar is not nearly as bad as having too little, but both are not ideal. Let’s take a look at why this is the case.

Too Much Rebar

The number one main reason why using too much rebar is bad is because it’s just not economical. Rebar is very expensive, but using too much of it is going to end up costing you way too much money compared to the benefits that it brings to the table. Moreover, if there is too much rebar in place, the pouring and placement of concrete can become somewhat difficult.

Too Little Rebar

If rebar is not used at all or enough, the concrete becomes highly prone to cracking due to tension forces. In other words, not using enough rebar means that concrete is not reinforced enough to withstand extreme tension and pressure. Simply put concrete that doesn’t have enough rebar is going to be comparatively weak and unable to withstand extreme forces.

Are There Regulations Specifying How Much Rebar to Put in Concrete?

Yes, there are some regulations that specify how much rebar needs to be put in concrete. However, with that being said, the regulations differ from one area to another and from one country to another. Moreover, the regulations also depend on the specific type of building being constructed, particularly in terms of height, size, and weight.

When it comes to small residential buildings, such as if you were making a foundation for a garage, then there are typically no specific regulations to follow.

However, if you are building large commercial buildings, whether office buildings or large apartment blocks, then there are some regulations that you will need to look into. However, these differ widely and there are many factors that need to be considered, so this is not a topic that we can discuss in great detail today.

Mistakes to Avoid, Tips & Tricks

Lastly, let’s take a look at a couple of things to keep in mind when deciding how much rebar to use:

  • Concrete is a rather permanent kind of thing, so be sure to measure twice; once the concrete is poured, removing it to correct mistakes will be super costly and time-consuming
  • There are different types of rebar out there, both in terms of what they are made of and their sizes, so be sure to use the right one for the application at hand


As you can see, calculating how much rebar you need is not very difficult at all. Now, if you don’t feel confident in your own mathematical capabilities, you can always use an online rebar calculator. Yes, this is exactly what it sounds like, it is something where you can input your parameters and the program will automatically tell you exactly how much rebar you require for the project at hand.

Just remember that rebar and concrete are quite permanent, so be sure to always measure twice before you do anything.