Retaining Wall Block Calculator

Estimate retaining wall blocks, cap units, compacted base gravel, drainage stone behind the wall, drain pipe length, tonnage, waste, and optional material cost from editable wall and block assumptions.

Material estimator only. Retaining walls can fail from soil pressure, poor drainage, surcharge loads, slopes, frost, and weak foundations; follow approved plans, local code, and manufacturer instructions.

Wall and Block Inputs

Include any block height below finished grade.
Caps and Drainage
Base Gravel and Drainage Stone

Material Estimate

Wall blocks--
Courses x blocks/course--
Installed wall height--
Cap blocks--
Base gravel--
Drainage stone--
Total aggregate--
Drain pipe--
Estimated cost--
Face area--
SummaryEnter wall dimensions and calculate.

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Assumptions and Formulas

This calculator estimates material quantities for segmental retaining wall blocks. It does not check soil pressure, sliding, overturning, bearing, geogrid, frost, slopes, surcharge loads, or drainage outlet design. The default base and drainage values follow common manufacturer planning details: a compacted granular base and clean wall rock behind the blocks. One installation reference from Allan Block specifies a minimum 6 in wall-rock base and 12 in of wall rock behind the block, with drain pipe required for reinforced walls, gravity walls over 4 ft, or poor drainage sites.

installed height = exposed height + buried block allowance
courses = ceiling(installed height / block height)
blocks per course = ceiling(wall length / block face length)
wall blocks = ceiling(courses x blocks per course x (1 + waste %))
base gravel volume = wall length x base trench width x base depth
drainage stone volume = wall length x drainage stone width x drainage height
tonnage = order volume x aggregate density

Volumes are based on rectangular takeoffs. Curves, corners, step-ups, returns, geogrid zones, over-excavation, soil replacement, block core fill, and supplier rounding can change the order quantity.

Retaining Wall Estimating Guide

Block courses

Use the installed height, not only the exposed height. A buried base row or partial course still consumes blocks.

Base gravel

Base volume uses compacted dimensions. Order extra when the trench bottom is uneven or weak soil must be removed.

Drainage stone

Clean, free-draining stone behind the blocks reduces hydrostatic pressure only when it has a working outlet.

Caps and cuts

Caps are counted by wall length. Add more waste for curves, corners, miters, stairs, and exposed end cuts.

Example Calculation

A 40 ft long wall with 3 ft exposed height, 8 in buried allowance, 18 x 8 in block faces, and 5% block waste needs 6 courses and 27 blocks per course. The calculator estimates 171 wall blocks. With a 24 in wide by 6 in deep base, 12 in drainage stone behind the full installed wall height, and the default 10% aggregate allowance, it estimates about 1.63 yd3 of base gravel and 5.98 yd3 of drainage stone.

Retaining Wall Block FAQ

Should I include buried blocks in the block count?

Yes. Any block below finished grade should be included because it is part of the installed wall. Enter that depth as the buried block allowance.

What base depth should I use?

Use the depth from your block manufacturer or approved plans. The default 6 in base is a common planning value for segmental retaining wall systems, not a universal design rule.

What drainage stone width should I use?

Many segmental wall details use about 12 in of clean wall rock behind the block. Taller walls, reinforced walls, wet sites, or engineered designs may require different drainage zones.

Does the calculator include geogrid?

No. Geogrid length, vertical spacing, embedment, and strength depend on wall height, soil, loading, slopes, block system, and engineering requirements.

Why does tonnage vary by supplier?

Stone density changes with gradation, moisture, compaction, and local material. Use supplier density or tons-per-cubic-yard values for final orders.

Limits and Safety Notes

  • Last updated: June 27, 2026.
  • Privacy: inputs stay in your browser; the page does not upload calculator values.
  • Material basis: all dimensions, waste factors, densities, and costs are editable because block systems and suppliers vary.
  • Engineering note: this tool is not a substitute for permitted drawings, local code, site drainage design, or a qualified retaining wall professional.

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