Retaining Wall Calculator
Estimate the wall blocks, cap blocks, and gravel backfill your retaining wall needs.
Results are estimates for planning. Retaining walls hold back real loads — confirm height limits, drainage, and permits with your local building department.
How to Measure a Retaining Wall
The block count comes from the face area of the wall — its length times its exposed height.
Length and height
Measure the wall length in feet and the finished height in feet. Include the buried first course in the height; it counts toward the block total.
Block size
Pick your block size so the calculator can work out blocks per square foot. It also estimates cap blocks for the top course and gravel backfill behind the wall.
Common Mistakes to Avoid
- No drainage plan. Water pressure topples walls — gravel backfill and a drain pipe are not optional.
- Skipping the buried course. The first course should sit below grade on compacted gravel; count it in the height.
- Forgetting caps. Cap blocks finish the wall and protect the top course — budget them in.
- Building too tall. Walls over about 3-4 ft usually need an engineer and a permit. Check before you start.
Frequently Asked Questions
Multiply wall length by height for the face area, then by the blocks per sq ft for your block. A 12×8 in block is about 1.5 per sq ft.
Most segmental walls finish with cap blocks glued to the top course — roughly one per linear foot of wall.
A drainage zone of about 12 inches of gravel behind the blocks for the full wall height, plus a compacted base below.
Often about 3-4 ft for a DIY wall. Taller walls or sloped backfill usually need an engineer and a permit.
Water behind the wall adds huge pressure; gravel and a drain pipe let it escape so the wall isn't pushed over.