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Calculators / Hardscape

How many blocks for your retaining wall?

Put in the length and how tall it shows above ground. You'll get blocks, caps, gravel and drain pipe, and a straight answer on height.

These are example numbers. Put in yours.

Your wall

ft
ft

The part that shows. We add the buried course.

The block

Block face

What it holds back

Above the wall

Order this much

168 blocks

That's 8 courses of 12 x 4 in block plus 21 caps, with 2 courses buried. Under and behind it goes 4.5 tons of gravel.

Blocks
1688 courses × 20
Caps
21
Base gravel
1.5 tons0.7 cu yd
Drain gravel
3 tons2 cu yd, plus 20 ft pipe

courses = 24 in ÷ 4 in = 6 up, + 2 buried (6 in) = 8

per course = 20 ft × 12 ÷ 12 in = 20, rounded up

blocks = 20 × 8 × 1.05 waste = 168

caps = 20 × 1.05 = 21

base = 20 ft × 2 ft wide × 0.5 ft deep = 20 cu ft = 0.7 cu yd × 1.4 = 1.5 tons

drain gravel = 20 ft × 1 ft × 2.7 ft tall = 53.3 cu ft = 2 cu yd × 1.4 = 3 tons

pipe = 20 ft of 4 in perforated, plus the run to daylight

Buried course

Bury 2 courses below grade, 8 in. Dig the trench 14 in deep so the 6 in base fits under it.

Fabric

Line the dirt side of the drainage gravel with non-woven fabric so mud doesn't clog it.

See non-woven geotextile fabric on Amazon

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Drain pipe

Lay the pipe holes down at the back of the base, and run it out to daylight. Add that outlet run to the 20 ft.

Caps

Glue caps down with landscape block adhesive. Two beads per cap.

See landscape block adhesive on Amazon
Call 811

Call 811 a few days before you dig. They mark buried gas and power lines for free.

How we work it out

We count courses up the face, add the courses you bury, and multiply by the blocks in one course.

courses = height ÷ block height, + buried courses

blocks = (length × 12 ÷ block length) × courses × 1.05

Bury 1 in for every 8 in of wall, 6 in at least. The 5% covers broken blocks and cuts.

base gravel = length × 2 ft wide × 0.5 ft deep

drain gravel = length × 1 ft × wall height from the base

Over 4 ft of held-back soil, the IRC wants an engineered design. Same goes for a wall over 2 ft with a driveway or slope above it. Lots of towns measure from the bottom of the footing, and some permit anything over 3 ft. Call yours before you dig.

Where the numbers come from

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