Retaining Wall Calculator
Estimate the block count, cap count, and base gravel for a segmental retaining wall from its length, height, and block size — so you can price and order a garden or landscape wall with confidence.
How to Use
- Enter the wall length and finished height in feet to set the face area to build.
- Enter the block face width and height in inches — check the spec for the SRW unit you are using.
- Read the number of wall blocks needed; the tool divides the wall face by one block face.
- Note the cap count for the top course and the base gravel estimate for the footing trench.
- Use the Base & backfill notes to plan the compacted gravel base, drainage, and the 4-foot DIY height limit.
Show Work
Base & backfill
About the Retaining Wall Calculator
Working on building, materials estimation and site work? The Retaining Wall Calculator is a free browser tool that gives you the answer in seconds. Estimate the block count, cap count, and base gravel for a segmental retaining wall from its length, height, and block size — so you can price and order a garden or landscape wall with confidence.
How it works
Put each value in its box and read the answer as you go. Because it recalculates live, you can play with the inputs to see how each one moves the result — handy for checking your own working or planning ahead. Everything happens on your device, so it is fast and private.
Want the deeper story? The Knowledge Base explains the ideas behind the tools in more detail.
Frequently Asked Questions
How many blocks are in a retaining wall?
Divide the wall face area by the face area of one block. A 12-inch-wide by 4-inch-tall block covers about 48 square inches, so it takes roughly three of them per square foot of wall. The calculator does this from the length, height, and block dimensions you enter and adds a top course of caps.
How tall a wall can I build without an engineer?
As a general rule, segmental retaining walls up to about 4 feet of exposed height can be DIY without an engineered design, though local codes vary. Taller walls, walls holding back a slope, or walls with a surcharge (a driveway or structure above) usually need geogrid reinforcement and an engineer's stamp.
What goes under and behind the wall?
Start with a compacted gravel base trench, typically about 6 inches deep and wider than the block, leveled carefully since the whole wall rides on it. Behind the wall, add free-draining gravel backfill and a perforated drain pipe at the base so water pressure cannot push the wall over.
Do I need cap blocks?
Caps finish the top course, give a clean edge, and are usually glued down with masonry adhesive to resist tampering and weather. The calculator counts one row of caps along the wall length. Some block systems are self-capping, in which case you can ignore that figure.
How much base gravel will I need?
The estimate here covers the leveling-pad trench under the wall. For a full job also budget for the free-draining gravel behind the wall, which can be a larger volume than the base itself. Use a gravel calculator to convert the trench and backfill dimensions into tons or cubic yards.
How do I use the Retaining Wall Calculator?
Just type your numbers. The answer shows up right away — there is no button to press. Change anything and it updates by itself.
Do I need to install or sign up for anything?
Not at all — it runs in the browser with nothing to install and no account. After it loads once, it even works without an internet connection.
Is my information private?
Yes. Everything happens in your browser. Nothing you type is sent to a server or saved anywhere.
Common Use Cases
Building a garden wall
Turn wall length and height into block and cap counts so you order the right pallets for a landscape wall.
Edging a raised bed
Size a low border or raised planting bed with larger blocks and get a quick material count.
Terracing a slope
Estimate blocks for a wall that holds back grade, keeping within the DIY height limit.
Pricing a hardscape job
Get block, cap, and base figures up front to quote a retaining wall before ordering.
Planning the base trench
See the base gravel estimate to dig and prep a properly compacted footing for the wall.
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