Retaining Wall Calculator – Estimate Block & Backfill
Calculate how many retaining wall blocks you’ll need and how much base and backfill gravel is required to build a wall. Optionally enter the price per block to get a cost estimate.
Wall Block Material Estimate:
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How to Calculate Retaining Wall Materials
You can use many materials to build retaining walls, but people often use wall blocks or timbers for the construction.
To estimate retaining wall materials using the calculator above, enter the wall’s length and width and the preferred block dimensions.
Find Qualified Retaining Wall Professionals in Your Area
If you’re using a different block style for the cap row, then enter those dimensions separately to get a separate estimate for the cap blocks. You can also add the price per block to estimate the retaining wall cost.
Keep reading to learn the formulas to calculate retaining wall materials yourself.
Note: Estimating material for concrete block walls is a bit different. If you’re building a concrete block wall, then try our concrete block calculator.
How Many Retaining Wall Blocks Do You Need
To estimate the total number of retaining wall blocks, you’ll first need to calculate the number of rows and columns needed for the wall.
Step One: Take Measurements for the Wall
Start by measuring the wall’s width and height. Most experts suggest embedding the first course of blocks below grade about 10% of the wall height to support it correctly.
For example, if the desired wall height is 6 feet, you should embed it below grade by 7-8 inches. Be sure to account for this when measuring the wall height.
Step Two: Calculate the Rows and Columns
Divide the wall’s width in inches by the block width and round up; this is the number of columns. Divide the wall’s height in inches by the block height and round up; this is the number of rows.
Formulas to Calculate Rows & Columns
wall columns = wall width / block width
wall rows = wall height / block height
Step Three: Calculate the Retaining Wall Blocks Needed
To find the total number of blocks needed for the wall, multiply the number of columns by the number of rows; don’t forget to subtract a row if using cap blocks.
Formula to Calculate Blocks
total blocks = rows × columns
Calculate Cap Blocks
If the top row will be a cap block, then the number of cap blocks needed is equal to the number of columns found above.
Retaining Wall Estimation Tips
When ordering supplies, it’s a good idea to plan for additional retaining wall materials, including blocks and cap blocks to account for waste or bad material. We suggest ordering an extra 10% of materials to accommodate this, but the project’s complexity might require more or less.
Don’t forget to account for embedding the first course of blocks below grade when measuring the desired wall height. Accounting for this from the start will ensure that the wall does not end up too short.
If the wall is too high, you may need to embed it deeper in the ground to reach the desired height; this requires a little more digging but is otherwise ok. See our retaining wall cost guide to find the average price of a retaining wall.
Preparing the Retaining Wall Base
Most experts suggest embedding the retaining wall below grade on a level base of 6″ gravel or stone. They also suggest making the base twice as wide as the block depth to account for settling.
The calculator accounts for this in the material estimate, but you can also use our gravel calculator to estimate 6″ of gravel for the project.
During the installation, it’s critical to ensure that the retaining wall base is compacted and level so that the first course of the block will be level.
How to Estimate Backfill Gravel
The retaining wall should have 12″ of gravel immediately behind the entire wall to allow for proper drainage. The calculator above will estimate this or, you can use our cubic yards calculator to calculate this separately.
Don’t forget that you’ll also 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 pores of the gravel, making it less effective. Be sure to get this when purchasing material.