Retaining Wall Calculator

Blocks (any size), poured concrete, timber, or stone — with caps and base gravel.

You'll need

90 blocks

Wall face area

60 sq ft20' long × 3' high

Wall blocks

90Concrete block — standard (≈16×6" face)

Cap blocks

20~12" cap units

Gravel base / backfill

1.0 tons6"-deep leveling base + drainage backfill

Block cost (est.)

$450~$5/block material

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A retaining wall holds back soil and turns a slope into flat, usable yard. The most popular DIY type is a segmental concrete block (SRW) wall — and the steps below cover it — but walls can also be poured concrete, stacked timber, or natural stone, so the calculator lets you pick the material and switches its math to match. Under about 4 feet, a block wall is a strong weekend project; the secret is a level, compacted base course and gravel backfill with drainage so water pressure never builds behind the wall.

DifficultyIntermediate

TimeA weekend for a short wall; longer for tall or curved runs

SkillsHeavy lifting and meticulous leveling of the first course

PermitsWalls over ~4 ft (or any wall holding up a structure/driveway) usually require an engineered design and a permit. Check before you build tall.

Tools you'll need

Plate compactor
Shovel and wheelbarrow
4-ft level
Rubber mallet
Masonry saw or block splitter
Landscape fabric and drain pipe

Step by step

Dig the base trenchExcavate a trench wide enough for the block plus backfill, deep enough to bury the bottom course (and below frost for tall walls).
Compact a gravel baseAdd and compact ~6" of gravel, then screed it dead level — every block above follows this course.
Set the first course perfectly levelLay the base blocks, checking level front-to-back and side-to-side on every one. Slow here saves the whole wall.
Stack and backfill with gravelStack courses with the built-in setback, sweep block tops clean, and backfill behind each course with drainage gravel (wrap a perforated drain pipe in fabric at the base).
Cap itGlue cap blocks on with masonry adhesive for a finished top edge.

Common mistakes

An unlevel first course

Errors multiply up the wall. Spend the time to get the base course perfect in both directions.

No drainage gravel or pipe

Soil behind a wall holds water, and water pressure pushes walls over. Backfill with gravel and add a drain pipe.

Building too tall without engineering

Walls over ~4 ft need engineering and often geogrid reinforcement and a permit. Don't freehand a tall wall.

Safety

Blocks are heavy — lift with your legs and use a hand truck.
Wear eye protection when cutting block.

Frequently asked questions

How tall can a DIY retaining wall be?

Generally up to about 3–4 ft. Taller walls need an engineered design, soil reinforcement (geogrid), and usually a permit.

How much material do I need?

Pick your wall material above — concrete block (small, standard, or large face), poured concrete, timber, or natural stone — then enter length and height. The calculator switches its math to match: block and cap counts, cubic yards of concrete, 6×6 timbers, or tons of stone, plus base gravel for all of them.

What size are retaining wall blocks?

Segmental block faces vary a lot by product — small units are roughly 12×4", standard around 16×6", and large units up to 18×8" or more. The calculator includes presets for each; check your specific block's coverage on the label.

Do I need drainage behind the wall?

Yes. Gravel backfill plus a perforated drain pipe at the base relieves water pressure that would otherwise topple the wall.