Retaining Wall Calculator

Calculate how many segmental blocks a retaining wall needs, plus its gravel base volume.

⏱ Updated: 18 Sep 2026

Calculator

Free retaining wall calculator: find how many segmental blocks a wall needs, plus its gravel base volume.

Blocks Needed
Wall Face Area (sq ft)
Gravel Base
yd³

Block count = wall face area ÷ block face area, rounded up and padded by the waste percentage for cuts and breakage. Gravel base sizing (6 in deep by default) is a common landscaping guideline for low walls — taller or load-bearing walls need an engineered base and should be reviewed by a professional.

Enter a wall's length and height, plus a block size, to calculate block count and gravel base volume.

How to Use the Retaining Wall Calculator

Enter the wall's length and height, pick a block preset or type in custom block face dimensions, then adjust the waste percentage and base trench size if the defaults don't match the actual product being used.

wall face area (sq ft) = wall length × wall height
block face area (sq ft) = (block height ÷ 12) × (block length ÷ 12)
blocks needed = ⌈(wall area ÷ block face area) × (1 + waste %)⌉

Waste isn't padding for its own sake — corners, curves, and courses that don't divide evenly into whole blocks all eat into a delivered pallet, and a 10% allowance covers most straight-run walls without leaving a stack of unused units behind. A wall with lots of corners or a curve typically needs to push that number higher.

Alongside block count, this Retaining Wall Calculator figures the compacted gravel base a segmental wall sits on — a trench the wall's length long, at whatever width and depth are set, converted straight to cubic yards.

base volume (yd³) = wall length × (base width ÷ 12) × (base depth ÷ 12) ÷ 27

The defaults here suit a low garden or landscaping wall. Anything retaining a significant slope, holding back a driveway, or built taller than a couple of feet carries real structural load and drainage requirements — geogrid reinforcement, a proper drainage aggregate, sometimes an engineered footing — that this calculator doesn't size. Get an engineer or a licensed contractor involved before building a wall like that.