Circle Retaining Wall Block Calculator
Planning a circular retaining wall for a garden bed, tree ring, or fire pit? Accurately estimating the number of blocks you'll need is the first step to a successful project. Our Circle Retaining Wall Block Calculator simplifies this process, helping you avoid multiple trips to the store and unnecessary waste. Simply enter the dimensions of your project and the blocks you're using to get an instant estimate.
Project Estimator
How to Use the Calculator
To get an accurate estimate, you'll need a few key measurements. All measurements should be in inches.
- Inner Diameter of Circle: Measure the distance across the widest part of the inside of your planned circle. This determines the circumference of your first course of blocks.
- Desired Wall Height: Measure from the base of the wall to your desired final height. This does not include any portion of the first course that will be buried for stability.
- Block Length: Measure the length of the front face of a single retaining wall block.
- Block Height: Measure the height of a single block.
- Include Capstones: Check this box if you plan to finish your wall with a top layer of capstone blocks. We assume one capstone per block on the top course.
Calculation Example
Let's say you're building a tree ring with the following specifications:
- Inner Diameter: 60 inches (5 feet)
- Desired Wall Height: 16 inches
- Block Length: 11.5 inches
- Block Height: 4 inches
- You do want to include capstones.
Based on these numbers, the calculator would determine you need approximately 17 blocks per course for a total of 4 courses. This results in a total of 68 wall blocks and 17 capstones for the top layer.
Understanding the Calculation
The calculator uses fundamental geometry to estimate your material needs. Here's a breakdown of the logic:
- Calculate Inner Circumference: The first step is to find the total length of the inside of your circle. The formula is:
Circumference = Inner Diameter × π (3.14159). - Determine Blocks Per Course: We then divide the circumference by the length of a single block. Since you can't use a fraction of a block, we round this number up to the nearest whole number:
Blocks Per Course = ceil(Circumference / Block Length). - Determine Number of Courses: To find out how many layers (courses) of blocks you'll need, we divide the total desired wall height by the height of a single block, again rounding up:
Number of Courses = ceil(Wall Height / Block Height). - Calculate Total Blocks: Finally, we multiply the number of blocks in each course by the total number of courses:
Total Blocks = Blocks Per Course × Number of Courses. If capstones are included, the number of capstones needed is equal to the number of blocks in one course.
Choosing the Right Blocks for a Circular Wall
Not all retaining wall blocks are created equal, especially when building curves. You have two main options:
Tapered Blocks
Tapered blocks are specifically designed for curves. They are wider in the front and narrower in the back. This shape allows them to fit together tightly in a circle without creating large gaps. For small, tight circles (like a fire pit), tapered blocks are almost essential for a professional-looking finish.
Rectangular Blocks
Standard rectangular blocks can also be used, but they present challenges. When laid in a curve, the front corners will touch while the back corners will be far apart. This creates V-shaped gaps between the blocks on the outside of the curve. For very large diameter circles, this may be acceptable, but for smaller projects, the gaps will be significant and may need to be filled with mortar or construction adhesive.
Pro Tip: When using this calculator with rectangular blocks, the result is still a very good estimate. However, be aware that you will have gaps on the outer face of the wall. The smaller your circle's diameter, the larger these gaps will be.
Frequently Asked Questions (FAQ)
Do I need to bury the first course?
Yes, for stability, you should always bury at least half of the first course of blocks in a compacted gravel trench. The "Desired Wall Height" in the calculator should be the height you want to see above ground.
What about backfill and drainage?
For any retaining wall taller than a single course, proper drainage is crucial. You should backfill behind the wall with gravel to relieve hydrostatic pressure and prevent bulging or failure. For taller walls, consider installing a perforated drainage pipe at the base.
Do I need construction adhesive?
Yes, it's highly recommended. Applying a bead of concrete/masonry construction adhesive between each course of blocks will lock them together, adding significant strength and stability to your wall.