Sawhorse Calc

Retaining wall calculator

Enter the wall length, how high it stands above the ground and your block size. You get blocks, caps, base gravel and drainage stone, with the buried first course already counted.

Wall and blocks

Starting figures are typical. Type the ones on your product or quote if you have them.

Cost (optional)

168 wall blocks

Courses, including buried
8
Blocks per course
20
Caps
20
Gravel base
0.59 cu yd, about 0.9 tons
Drainage stone behind
1.98 cu yd, about 3.0 tons

How to work it out

  1. Measure the length of the wall along the ground. For a curved wall, measure along the curve.
  2. Measure how high the wall will stand above the finished ground. The calculator adds the buried course for you.
  3. Enter the block face size and depth from the label. Common landscape blocks are about 12 in long and 4 in high.
  4. Enter the cap length, or 0 if you are not capping the wall.

How the wall is built up

PartTypical size
Buried first course10% of the wall height, at least 6 in
Gravel base under the blocks6 in deep, compacted
Base widthBlock depth plus 6 in in front and behind
Drainage stone behind the wall12 in wide, full height

These are common starting points. Your site, climate and supplier may call for something different.

What the numbers assume

These are common figures from block makers' installation guides for small gravity walls. Your block's own guide comes first: some ask for a deeper base, more burial or a drain pipe at the bottom of the drainage stone.

Taller walls need a design

Walls over about 4 ft, walls holding back a slope, a driveway or a building, and walls in poor or wet soil usually need geogrid reinforcement and an engineer's design, and often a permit. This calculator only counts materials; check with your local building department before you build.

Common questions

How many retaining wall blocks do I need?

Divide the wall length by the block length to get blocks per course, and the wall height by the block height to get courses. Add the buried course and about 5% extra. A 20 ft wall 2 ft high in 12 by 4 in blocks needs about 168 blocks.

How deep should the first course be buried?

A common rule is 10% of the wall height or 6 in, whichever is more. For a 2 ft wall that is 6 in; for a 5 ft wall, 6 in as well.

How much gravel do I need for a retaining wall base?

Enough for a trench about 6 in deep and as wide as the block plus 6 in on each side. The calculator works this out in cubic yards and tons.

What goes behind a retaining wall?

About 12 in of clean, angular drainage stone for the full height, often with a perforated drain pipe at the bottom, then soil on top. It stops water building up and pushing the wall over.

How tall can a retaining wall be without an engineer?

Rules vary by place. Many areas and block makers draw the line around 3 to 4 ft. Check your local code before building anything taller.

Doing this job for a customer? Turn your numbers into a free written estimate on QuoteToPaid.

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