How to Calculate Amount of Retaining Wall Materials Needed?

Retaining Walls as the name suggests retain backfill also they instantly enhance any landscape design. A retaining wall must have the strength to stand back the weight of soil, plants, and sometimes other structural member.

There are a variety of material we can use to build a retaining wall which includes wood, patio stones and poured concrete. Its cost varies depending upon the material used for the construction of retaining wall. Concrete poured retaining wall are among the most expensive one. Other types of retaining wall material include timber wood, stones and pavers.

Once you have decided to build a retaining wall then next step is to figure out and calculate all the material needed to complete this task. Having a landscaping estimate will help you plan for the cost of materials and manhours to build the retaining wall, which will help you save time, effort and money.

So, the number of concrete block or stone block and gravel needed depends on the dimensions of wall and depth of backfill space.  In this article, we will walk you through all the knowledge that might help you in finding all the materials needed to build an eye-catching retaining wall.

To estimate the total number of retaining wall block, we will first need to find out the number of rows and columns needed for the wall.

Table of Contents

Steps to Calculate the amount of Retaining wall Materials

  1. Take the Dimensions
  2. Calculate the required Rows and Columns
  3. Calculate the Retaining Wall blocks
  4. Find Out the Wall Square Footage
  • Calculate the Backfill Gravel

1. Take the Dimensions

First start by taking the measurements of the wall’s width and height. This can be done by using a measuring tape. While measuring the dimensions, experts suggest that embedding the first course of block grade about 10% of the wall height to support it correctly. To understand this concept, take an example of a wall with a height of 7 feet. Now to avoid any complications afterwards you should consider embedding it below 8-9 inches.

2. Calculate the required Rows and Columns

To calculate the required rows and columns, divide the wall’s width in inches by the block width and round up, this will give you the number of columns. Now divide the wall’s height in inches by the block height and round up, this will tell you the number of rows. The formula to calculate number of rows and columns is quite simple and easy. They are as follows:

                                                      Wall Columns = Wall Width/ Block Width

                                                       Wall Rows = Wall Height/ Block Height

3. Calculate the Retaining Wall blocks

To calculate the total number of blocks needed for the retaining wall, all we need to do is to multiply the number of columns by the number of the rows. While calculating the block be sure to subtract a row if you are using cap blocks.

                                                       Number of blocks = rows x columns

If you are using cap blocks, then the number of cap blocks required is equal to the number of columns found above, as long as the cap block being used have the same width as the field block. It is always a good practice to order additional supplies while constructing any structure.

4. Find Out the Wall Square Footage

In the market, some blocks are sold by the square foot and not by the number of blocks. Other may be sold by the pallet, with a specific number of square feet per pallet. This is true when you are buying a block material that is arranged in a pattern or other detailing. So, for this purpose you will need to find out the total square footage of the retaining wall you are planning to build. For this you will need to measure the width and height of the wall in feet or inches. The measurement should include the total height of the wall, including any block material that will be used sub-grade. Once you have the measurement then simply multiply them together. By any chance, if you are using feet unit for measuring the dimensions so this will the value in square feet for the wall. And if you are using inches unit then divide the value with the 144 to get the square footage for the retaining wall.

5. Calculate the Base Gravel

In general practice, it is always recommended to embed the retaining wall below grade on a level base of 6 inch of well compacted gravel or stone. It is also suggested to make the base twice as wide as block depth to account for setting. Observation shows that the compacted gravel can loose as much as 20% of its initial volume. While compaction chances are that the 6 inch of loose gravel may compact down to 4.8 inch. So, it is always advised to purchase an additional 20% supply of gravel when compacting to compensate for the loses. Now if you want to calculate the gravel in cubic yards for a base of 6 inches then you might want to learn how to do it.

                                              Cubic Yards = (wall depth x 2) x (Wall width) / 46,656

Make sure to keep all the dimensions in inches to get the correct value. Also add 20% extra to avoid complications.

6. Calculate the Backfill Gravel

Once you have everything taken care of, now it is time for you to immediately put 12 inches of gravel behind the wall to allow for the proper drainage. Also, you want to consider adding a layer of landscape fabric between the stone backfill and the earth behind it to prevent the dirt from filling the porous surface or holes along sides of the gravel. This will make the whole process less effective. Now you have all the information that will help to calculate all the supplies, measuring the dimensions and other units measurement value conversations need to build a long lasting and eye soothing retaining wall.

Retaining Wall Material Calculator

Here’s an online retaining wall material calculator that will help you in determine the different materials you need for a retaining wall:

Saad Iqbal is a professional civil engineering and freelance write. He's passionate about structures, construction management, and home improvement topics. He's been working as a Senior Engineer in a consultant firm for over 8 years. Besides he loves writing informative and in-depth content focused on construction and home-related topics. You can catch him at his linkedin page or reach out via our contact us page.

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