Paving & Walls
Retaining Wall Block Calculator
Enter the wall length and the height you want above the ground, the face size of your block and cap, how many courses go below grade, and the size of the base trench. You get blocks, caps, courses and gravel for the leveling base.
Worked example
- Blocks per course = 30 ft x 12 / 12 in = 30.
- Courses = 2 ft x 12 / 6 in = 4, plus 1 buried = 5.
- Blocks = 30 x 5 = 150; caps = 30.
- Gravel base: 30 ft x 24 in x 6 in = 1.11 cu yd.
Common sizes at a glance
| Size | Wall blocks | Cap blocks | Base gravel |
|---|---|---|---|
| 10 ft long, 1 ft tall | 30 | 10 | 0.37 cu yd |
| 20 ft long, 2 ft tall | 100 | 20 | 0.74 cu yd |
| 30 ft long, 2 ft tall | 150 | 30 | 1.11 cu yd |
| 50 ft long, 3 ft tall | 266 | 38 | 1.85 cu yd |
The buried course is part of the count
A segmental wall starts below the finished grade. At least one course sits in the trench so the bottom of the wall cannot slide out. People who count only the visible rows end up a full course short.
In the example, a 2 ft wall with 6 in tall blocks needs 4 visible courses plus 1 buried, so 5 courses of 30 blocks gives 150 blocks.
Measure along the face
Run your tape along the line where the front of the wall will sit. For a curved wall, lay a garden hose on the curve and measure the hose. Corners and steps in height change the count a bit, so add a few blocks for each turn.
Use the face length and face height of the block, not its depth. Most landscape blocks list these on the pallet tag. Caps are counted by their own length, which is why the example gets 30 caps for 30 ft of wall.
Base trench gravel
The first course sits on a compacted gravel pad, wider than the block is deep. The calculator multiplies trench length, width and gravel depth: 30 ft x 24 in x 6 in gives 1.11 cu yd.
Gravel behind the wall for drainage is a separate quantity. Many walls also need a perforated drain pipe at the base. Neither is included here.
- Leveling base: compacted crushed stone
- Drainage fill behind the blocks: clean stone, measured separately
- Cap adhesive: check the tube label for feet covered per tube
Height limits and who signs off
This tool counts materials only. It does not check whether a wall will hold the soil behind it. Taller walls, walls near driveways or slopes, and walls holding back a building load often need a permit and an engineered design, and the local building code and a licensed professional have the final word.
For a budget with your block price and mason labor time, use the retaining wall cost calculator. If the wall frames a patio, the paver calculator sizes the surface.
Questions
How many retaining wall blocks do I need for a 50 ft wall that is 3 ft tall?
The common sizes table on this page shows 266 wall blocks, 38 caps and 1.85 cu yd of base gravel for that wall. Your own block size changes the count, so enter it above.
Do I need caps on a retaining wall?
Caps finish the top course and keep water out of the hollow cores. Most block systems sell matching caps.
Does the count include waste?
Add a few blocks for corners, steps and breakage, since block walls have little cutting but pieces chip in handling.
How this works: formulas and typical values are listed on our method page; every data source and its license is on sources.
Last reviewed November 2026.