UseCalcPro
Home
MathFinanceHealthConstructionAutoPetsGardenCraftsFood & BrewingTools
Blog
  1. Home
  2. Construction

Retaining Wall Calculator

Calculate blocks and materials for retaining walls

Total Blocks

90

Courses

6

Estimated Cost

$345.00

Units
Wall Blocks
90
blocks needed
Courses
6
15 per course
Cap Blocks
15
cap blocks
Total Cost
$345.00
blocks only

Material Quantities

Wall Blocks90
Cap Blocks15
Gravel (yd³)2.96
Additional Materials
Total Gravel:2.96 yd³
Drain Pipe:20.0 ft
Filter Fabric:120.0 sq ft
Cost Breakdown
Wall Blocks$270
Cap Blocks$75

Example Calculations

1Garden Retaining Wall (20 ft × 3 ft, Standard Blocks)

Inputs

Length20 ft
Height3 ft
Block SizeStandard (16 × 6 in)
Cap BlocksYes
Base Gravel6 in deep × 24 in wide
DrainageYes (12 in deep)
Cost per Block$3.00
Cost per Cap$5.00

Result

Wall Blocks90
Courses6
Blocks/Course15
Cap Blocks15
Total Gravel2.96 yd³
Estimated Cost$345

Courses = 36/6 = 6. Blocks/course = 240/16 = 15. Wall blocks = 90. Cap = 15. Base gravel = 20×2×0.5/27 = 0.74 yd³. Drainage = 20×1×3/27 = 2.22 yd³. Cost = 90×$3 + 15×$5 = $345.

2Hillside Wall (30 ft × 4 ft, Large Blocks)

Inputs

Length30 ft
Height4 ft
Block SizeLarge (18 × 8 in)
Cap BlocksYes
Base Gravel6 in deep × 24 in wide
DrainageYes (12 in deep)
Cost per Block$5.00
Cost per Cap$7.00

Result

Wall Blocks120
Courses6
Blocks/Course20
Cap Blocks20
Total Gravel5.56 yd³
Estimated Cost$740

Courses = 48/8 = 6. Blocks/course = 360/18 = 20. Wall blocks = 120. Cap = 20. Base gravel = 30×2×0.5/27 = 1.11 yd³. Drainage = 30×1×4/27 = 4.44 yd³. Cost = 120×$5 + 20×$7 = $740.

Frequently Asked Questions

Q

How many blocks do I need for a retaining wall?

Divide wall height by block height to get courses, and wall length by block length to get blocks per course. Multiply courses × blocks/course. A 20 ft × 3 ft wall with 16×6" blocks: 6 courses × 15 blocks = 90 wall blocks plus 15 cap blocks.

  • Standard block (16" × 6"): 12 blocks per linear foot of height per 10 ft of wall
  • Large block (18" × 8"): 9 blocks per linear foot of height per 10 ft of wall
  • Cap blocks: 1 per block width along the top course (15 caps for 20 ft wall)
  • Add 5–10% extra for breakage and cuts at corners
  • Each standard block weighs 30–45 lbs; plan for heavy lifting or equipment
Block SizeWeightCoverage per BlockPrice Each
Standard (16" × 6")30–35 lbs0.67 sq ft face$2.50–$4.00
Large (18" × 8")45–55 lbs1.00 sq ft face$4.50–$7.00
Jumbo (24" × 8")60–80 lbs1.33 sq ft face$6.00–$10.00
Cap block15–25 lbsTop course only$3.00–$6.00
Q

How much gravel do I need behind a retaining wall?

Use 6 inches of compacted gravel for the base (width = 24 inches) and 12 inches of drainage gravel behind the wall full height. For a 20 ft × 3 ft wall: base = 0.74 yd³, drainage = 2.22 yd³, total ≈ 3 cubic yards.

  • Base gravel: 6" deep × 24" wide along full wall length
  • Drainage backfill: 12" deep behind wall for the full wall height
  • 3/4" clean crushed stone is ideal for both base and drainage
  • Gravel weighs ≈1.4 tons per cubic yard – plan for delivery truck access
  • Use non-woven geotextile fabric between gravel and soil to prevent clogging
Q

How much does a retaining wall cost per foot?

Retaining wall materials cost $15-40 per linear foot per foot of height. Small walls (2 ft): $15-25/ft, medium (3-4 ft): $25-50/ft, large (5+ ft): $50-100/ft. Installation labor adds $20-40 per sq ft of wall face.

  • DIY materials only: $10–$25 per sq ft of wall face
  • Professional installation: $25–$60 per sq ft of wall face (labor + materials)
  • 20 ft × 3 ft wall DIY cost: $300–$500 in materials
  • 30 ft × 4 ft wall professional cost: $3,000–$7,000 installed
  • Engineering fees for walls over 4 ft: $500–$2,000 additional
Wall HeightDIY Material Cost/ftPro Installed Cost/ftPermit Needed?
2 ft$15–$25$40–$70Usually no
3 ft$25–$40$60–$100Varies by jurisdiction
4 ft$35–$55$80–$140Usually yes
6 ft+$60–$100$150–$250Yes + engineering
Q

Does a retaining wall need drainage?

Yes, drainage is critical for retaining walls. Install perforated drain pipe at the base, 12 inches of gravel backfill behind the wall, and filter fabric to prevent soil from clogging the gravel. Poor drainage causes wall failure.

  • 4" perforated PVC drain pipe at the base, sloped 1% toward daylight outlet
  • 12" of 3/4" crushed stone backfill behind the wall, full height
  • Non-woven geotextile filter fabric wraps the gravel to block soil migration
  • Weep holes every 6–8 ft if no continuous drain pipe is used
  • Hydrostatic pressure from trapped water is the #1 cause of retaining wall failure

Related Calculators

Concrete Calculator

Calculate concrete amounts

Gravel Calculator

Calculate gravel needed

Block Count Calculator

Calculate CMU cinder block quantity for wall projects. Enter wall dimensions, block size, and openings to estimate total blocks, mortar, and material cost.

Brick Calculator

Calculate how many bricks you need for walls, patios, and projects. Enter wall dimensions and brick size to get accurate material and mortar estimates.

Backsplash Tile Calculator

Calculate backsplash tiles, material costs, and labor estimates for your kitchen. Covers subway, mosaic, porcelain, glass, and natural stone tile types.

French Drain Calculator \u2014 Estimate Gravel, Pipe & Cost

Calculate French drain materials including gravel, pipe, and landscape fabric. Compare DIY vs professional costs with soil type adjustments for your project.

Related Resources

How Much Does a Retaining Wall Cost in 2026? (By Material & Height)

Read our guide

How Many Tiles Do I Need? Tile Calculator Guide for Floors & Walls

Read our guide

How to Build a Deck: Complete Materials & Cost Calculator Guide

Read our guide

Concrete Calculator

Calculate concrete needed

Gravel Calculator

Calculate gravel amounts

Fence Calculator

Calculate fence materials

More Construction Calculators

Calculate materials for your building projects

View All

Last Updated: Mar 11, 2026

This calculator is provided for informational and educational purposes only. Results are estimates and should not be considered professional financial, medical, legal, or other advice. Always consult a qualified professional before making important decisions. UseCalcPro is not responsible for any actions taken based on calculator results.

UseCalcPro
FinanceHealthMath

© 2026 UseCalcPro