Free Landscape Calculator

Retaining Wall Calculator

Calculate exactly how many retaining wall blocks, cubic yards of gravel backfill and cost for your landscape retaining wall. Instant results with 5% waste factor included.

🧱
Retaining Wall Calculator
Blocks, gravel backfill and cost
Wall Dimensions
ft
ft
ft
📐 Your Results
—
Blocks Needed
With 5% waste
—
Wall Sq Ft
Total face area
—
Cu Yds Gravel
Backfill needed
Estimated Cost
Block + gravel estimate
$—
💡 Always order 10–15% extra for waste and settling.

📊 Understanding Your Results

Blocks Needed — Total retaining wall blocks including 5% waste for cuts. Order full pallets for best pricing (60–100 blocks per pallet).

Wall Square Feet — Total face area of your wall. Used for material quantities and contractor quotes.

Gravel Backfill — Cubic yards of crushed stone needed behind the wall for drainage. Proper drainage is critical — walls without it fail from hydrostatic pressure.

How the Retaining Wall Calculator Works

Our calculator determines block count by dividing wall face area by individual block area, then adding 5% waste. The gravel backfill estimate is based on a standard 12-inch drainage layer — the minimum required for wall stability. Walls over 3 feet tall typically require permits.

The Retaining Wall Formula

Step 1: Wall Face Area (sq ft) = Length × Height
Step 2: Blocks = (Face Area ÷ Block Face Area) × 1.05 waste
Step 3: Gravel Backfill (cu yds) = (Length × 1 ft depth × Height) ÷ 27
Step 4: Base course is buried — add 1 extra course to height

Example: 20 ft × 3 ft wall with 6″H × 12″L blocks = 60 sq ft ÷ 0.5 = 120 blocks × 1.05 = 126 blocks. Gravel: 2.2 cu yards.

Retaining Wall Height Guide

Wall HeightPermit NeededEngineer NeededDIY Feasibility
Under 2 feetUsually NoNo✅ Easy DIY
2–3 feetSometimesNo✅ Moderate DIY
3–4 feetOften YesSometimes⚠️ Experienced DIY
Over 4 feetYesUsually Yes❌ Hire contractor

Frequently Asked Questions

Common questions about retaining wall construction and materials.

How many blocks for a 20-foot wall at 3 feet high?
126 blocks for visible wall + 20 blocks for buried base course = 146 blocks total. Order 2 full pallets (60–80 blocks each). At $2.50/block = approximately $365 in materials.
How deep should a retaining wall base be?
6 inches of gravel + one full block height buried below grade. Total trench depth approximately 12–14 inches. The buried base prevents sliding and is the most important structural element.
What is the best material for a retaining wall?
Concrete segmental blocks (Allan Block, Versa-Lok) are most popular for DIY — interlocking design, no mortar, widely available. Natural stone is most attractive but expensive. Timber is cheapest but rots in 10–15 years.
How much does a retaining wall cost per linear foot?
DIY concrete block: $10–$50 per linear foot (materials only). Professional installation: $25–$150 per linear foot including excavation and labor.
Why do retaining walls fail?
Three main causes: 1. Poor drainage — always use gravel backfill and drain pipe. 2. Insufficient base depth — always bury at least one full block course. 3. No batter — set each course 0.5–1 inch back from course below.

💡 Wall Building Tips

Bury one full block course below grade — never skip this step.

Set each course 0.5–1 inch back for proper batter.

Use gravel backfill only — never clay behind walls.

Install a 4″ perforated drain pipe at wall base.