Retaining Wall Block Calculator

Blocks, caps, base, and backfill — the whole wall order from two measurements.

Your wall

Wall length (ft)

Exposed height (ft) Height above grade — burial is added automatically.

Block size Block sizes vary by brand — enter yours.

Face W (in)

Face H (in)

Depth (in)

Cap row

Waste factor

Materials list

Generated by AllUnits.io — allunits.io/calculators/retaining-wall

How this calculator figures it

Base and burial follow the Allan Block installation guide: a minimum 6-inch compacted gravel base, the first course buried 1 inch for every 8 inches of exposed wall height, and wall rock placed and compacted 12 inches behind the wall. Block counts divide wall face area by your block's face dimensions — segmental block sizes vary by brand, so the calculator uses the dimensions you enter.

How it works

buried courses = ceil( (exposed ÷ 8) ÷ block H ), min 1 · courses = (exposed + burial) ÷ block H

base = 6" deep × (block depth + 6") wide × length · drainage = 12" × wall height × length

Worked example — 20 ft of wall with 24 inches exposed in 12×4×8 block: burial needs 3 inches, which rounds up to one 4-inch course, so the wall stands 7 courses of 20 blocks — 147 with 5% waste — plus 20 caps. The base trench takes 0.43 yd³ of gravel (about 0.6 tons) and the drainage zone behind the wall 1.73 yd³ (about 2.4 tons). The trench width used here (block depth + 6") is approximate; Allan Block specifies the 6-inch compacted base depth firmly.

Retaining wall FAQs

How much of the wall gets buried?

1 inch per 8 inches of exposed height, minimum one full course — Allan Block guidance.

How tall can I build without an engineer?

Most systems and codes draw the line around 3–4 ft; taller or surcharged walls need engineering and usually a permit.

Do I need a drain pipe?

Allan Block requires one for reinforced walls, gravity walls over 4 ft, or poor-drainage sites.

What gravel for base and backfill?

Compactable crushed wall rock per the block manufacturer; confirm gradation with your supplier.

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Related calculators & sources

Pricing the base and backfill gravel separately? Use the Gravel Calculator. Paving above the wall: Paver Calculator. Mortared block walls: Concrete Block Calculator. Installation guidance is cited at Allan Block sources; convert measurements with the area and weight converters.

Estimates for planning and purchasing. Not engineering or code-compliance advice — confirm structural work with your local building department.