Retaining Wall Calculator
Count retaining wall blocks per course and total, plus cap blocks and gravel backfill volume.
Processed locally in your browser — nothing is uploaded.
Retaining Wall Calculator
Enter the wall dimensions to estimate blocks.
About Retaining Wall Calculator
From the wall length and height and a block face size (12 × 4 in default), it computes blocks per course, the number of courses, and the total with waste. It adds one course of cap blocks and sizes the gravel backfill assuming a 12 in drainage zone behind the full wall face.
Common uses
- Order block and drainage rock for a garden terrace wall
- Compare block counts between 12 in and 16 in block formats
Example
Input
20 ft long × 3 ft tall, 12×4 in blocks, 10% waste
Output
20/course × 9 courses = 180 → buy 198 + 20 caps · 2.22 yd³ backfill
Limitations
- Walls above ~3–4 ft typically require engineering and permits
- Ignores the buried base course and leveling pad — add one course and base gravel
Frequently asked questions
How many blocks do I need for a retaining wall?
Divide the wall length by the block face length for blocks per course, multiply by the number of courses (wall height ÷ block height), then add waste. A 20 ft wall, 3 ft tall, in 12×4 in blocks is 20 per course × 9 courses = 180 blocks, about 198 with 10% waste.
Do I need gravel behind a retaining wall?
Yes — a free-draining gravel zone behind the wall relieves the water pressure that topples most failed walls. This calculator sizes it at a 12 in depth behind the full wall face; pair it with a drain pipe at the base on taller walls.
How tall can I build a retaining wall without an engineer?
Many jurisdictions allow unengineered gravity walls up to 3–4 ft measured from the bottom of the base; anything taller, tiered, or carrying a slope or driveway above it typically needs engineering and a permit. Check your local code before you order block.
Should the first course of blocks be buried?
Yes — standard practice buries roughly 10% of the wall height (at least one course) below grade on a compacted gravel leveling pad. This calculator counts only the visible wall, so add one extra course plus pad gravel to your order.
Does this calculator upload my wall dimensions?
No. Block, cap, and backfill quantities are computed in your browser — nothing you enter is transmitted or kept on a server.