Retaining Wall Calculator
Calculate retaining wall blocks per course and total courses including the buried base, plus cap blocks, pallets, base gravel, drainage stone and backfill.
Blocks per course = wall length ÷ block length; courses = exposed height ÷ block height, plus the buried base course that stops the wall from kicking out. A 12 × 4 in unit gives three blocks per square foot of face, so a 30 ft wall 3 ft high is 30 per course over 10 courses — 300 units before waste, including the buried course. Base and drainage volumes come straight from the trench dimensions you enter, priced at roughly 100 lb/ft³ of crushed stone. Block setback slightly shortens the upper courses, which this ignores. Walls over about 4 ft, or any wall with a slope or a driveway above it, need an engineer — this is a materials estimate, not a design.
What is the Retaining Wall Calculator?
The ByteTools Retaining Wall Calculator counts a segmental block wall from the trench up. Enter the wall length and the height you want to see above grade, choose a block size, and it returns blocks per course, the number of courses including the buried base, the total units and caps, the pallets that comes to, and the stone volumes for the base and the drainage zone.
- Blocks per course and total courses including the buried base course
- Cap block count, waste allowance and pallet quantities
- Base gravel from the trench dimensions in cubic yards, cubic metres and tons
- Drainage stone behind the wall and backfill volume behind the blocks
- Presets for garden wall units through to large SRW blocks, imperial and metric
- Runs entirely in your browser with nothing uploaded
How to use the Retaining Wall Calculator
- 1
Choose imperial or metric and enter the wall length and the exposed height above grade.
- 2
Pick a block size, then adjust the block length, height and depth if yours differ.
- 3
Set how many base courses are buried and whether the wall is finished with cap blocks.
- 4
Enter the base trench width and depth, the drainage stone width and the blocks per pallet.
- 5
Read the blocks per course, total blocks, caps, pallets, and the base, drainage and backfill volumes with costs.
About the Retaining Wall Calculator
The ByteTools Retaining Wall Calculator counts a segmental block wall from the trench up. Enter the wall length and the height you want to see above grade, choose a block size, and it returns blocks per course, the number of courses including the buried base, the total units and caps, the pallets that comes to, and the stone volumes for the base and the drainage zone.
Blocks per course is simply wall length divided by block length, and courses is exposed height divided by block height plus the buried base course that stops the wall from kicking out at the bottom. A 12 by 4 in garden wall unit gives three blocks per square foot of face, so a 30 ft wall 3 ft high runs to 300 units over ten courses.
Everything is calculated in your browser and nothing is uploaded. Walls over about four feet, and any wall with a slope, a surcharge or a driveway above it, need an engineer and usually geogrid — this is a materials estimate, not a design. Block setback also shortens the upper courses slightly, which the count ignores.
Frequently asked questions
How many blocks do I need for a retaining wall?
Blocks per course is the wall length divided by the block length, and courses is the exposed height divided by the block height plus one buried base course. A 30 ft wall 3 ft high built from 12 by 4 in units needs 30 per course over 10 courses, or 300 blocks before waste.
How deep should a retaining wall base be?
Bury at least one full course, and dig six inches of compacted crushed stone under it in a trench about a foot wider than the block. Taller walls need more burial — a common guide is one-tenth of the wall height — and every manufacturer publishes its own figure.
How much drainage stone goes behind a retaining wall?
About 12 inches of free-draining crushed stone the full height of the block, with a perforated drain pipe at the bottom running to daylight. Water pressure behind a wall is what pushes it over, so the drainage zone is not the place to economise.
Do I need cap blocks on a retaining wall?
Caps are not structural but they finish the top course, shed water and stop the hollow cores from filling with debris. They are usually glued down with construction adhesive. Untick the cap option here if you are using a different coping detail.
How tall can a retaining wall be without an engineer?
Many jurisdictions set the threshold at four feet of exposed height, but the number varies and a shorter wall can still need design if there is a slope or a driveway above it. Check with your local building department before you order — this calculator counts materials, it does not certify a wall.
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