Enter your wall length and height to find out how many blocks and cap blocks you need — plus base gravel — with a waste factor and total cost.
A retaining wall is built in courses — horizontal rows of blocks stacked on top of each other. To find the block count you work out how many blocks fit in one row, how many rows make up the height, and multiply. This calculator adds the cap row, a waste allowance, and an estimate of the compacted gravel base the wall sits on.
1. Blocks per course = wall length ÷ block length, rounded up.
2. Courses = wall height ÷ block height, rounded up.
3. Wall blocks = blocks per course × courses, × (1 + waste %).
4. Cap blocks = one extra row along the top (if selected).
A retaining wall is only as good as its base. Dig a level trench, then add about 6 inches of compacted gravel and bury the first course roughly one-tenth of the wall's height. This spreads the load and stops the wall from settling or leaning. The calculator estimates base gravel from your wall length and a trench about twice the block depth wide.
Short garden walls (under about 3–4 ft) are a common DIY project. But taller walls — or any wall holding back a slope, driveway, or structure — face serious soil pressure and usually require drainage, geogrid reinforcement, and an engineer's design to meet code. Always check local requirements before building.
| Block (L × H) | Per 20 ft course | Notes |
|---|---|---|
| 12 × 4 in | 20 blocks | Low garden walls |
| 12 × 6 in | 20 blocks | Very common |
| 18 × 8 in | 14 blocks | Larger walls |