How Much Stone Do I Need for a Retaining Wall?

Understanding Retaining Wall Stone Requirements

A retaining wall is more than just a functional enhancement! A retaining wall provides soil retention, prevents drainage problems and is aesthetically pleasing to your landscape design, but the construction of a retaining wall requires careful planning to determine how much stone you will need, otherwise you risk delays or paying for stone that you never actually use. This blog serves to show you how to measure correctly and select the correct stone type for every aspect of the wall.
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Best Types of Stone for Retaining Walls

Landscape Barn recommends the following stone types for constructing a retaining wall:

• Wall Blocks or Cut Stone: These stones are designed specifically for walls and are meant to be interlocked or stacked together as efficiently/securely as possible for long-lasting stability.
• Crushed Stone (3/4"): Proper drainage behind the wall is very important, and crushed stone is the great material for backfill behind the wall, so that excess water can continue to drain through the stone, and not build up/compromise the integrity of the wall.
• Stone Dust: Useful for leveling the base course of your wall, which will greatly assist in your installation so that it's level throughout.
• Boulders: A great material for retaining walls that employs a rustic, natural character and/or a larger style accentuating visual intrigue.

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1-1/4" Crushed Stone

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3/4" Crushed Stone

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Stone Dust

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49"+ Boulders

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18"-48" Boulders

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3/8" Crushed Stone

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Planning Your Retaining Wall Area

Before purchasing any material, take time to complete a thorough design of the size and purpose of your wall. Consider the slope of your property and soil conditions, as well as whether the wall itself is decorative or load-bearing.

Measuring Wall Dimensions

Use a measuring tape to measure the length, height, and thickness (depth) of that wall. Multiply these numbers together to find the total volume of stone that you'll need to order. When measuring and completing the math, always round up. If your wall is taller, you may need to consider step terraces or reinforced sections of the wall.

Recommended Base Depth and Backfill

• Base: Dig a trench at least 6-8 inches deep, packed with compacted 3/4" crushed stone for stability. A solid base prevents shifting and helps the wall last longer.
• Backfill: Fill a minimum of 12 inches behind the wall with crushed stone to allow proper drainage. For taller walls, adding a perforated drain pipe is highly recommended.

Calculating How Much Stone You Need

Once you have your measurements, you can estimate how much material you will use.

Volume Formula (Length × Height × Depth)

To find wall stone volume: Length (ft) × Height (ft) × Depth (ft) = cubic feet. Divide by 27 to convert to cubic yards.

Converting Volume to Tons

Most stone weighs around 1.4 to 1.6 tons per cubic yard. Multiply cubic yards by this factor to estimate weight.

Example Estimates by Common Wall Sizes

• 10 ft wall, 2 ft high, 1 ft deep
  Volume: 10 × 2 × 1 = 20 cubic feet → 0.74 cubic yards
  Approx. 1.1 tons
• 20 ft wall, 3 ft high, 1 ft deep
  Volume: 20 × 3 × 1 = 60 cubic feet → 2.22 cubic yards
  Approx. 3.1 tons
• 30 ft wall, 4 ft high, 1.5 ft depth
  Volume: 30 × 4 × 1.5 = 180 cubic feet → 6.67 cubic yards
  Approx. 9.3 tons
• 40 ft wall, 6 ft high, 2 ft depth
  Volume: 40 × 6 × 2 = 480 cubic feet → 17.8 cubic yards
  Approx. 24.9 tons

These estimates are starting points. Walls with curves, steps or irregular designs may require additional material.
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Installation Tips

Site Preparation and Base Course

Excavate at least 6-8 inches. Lay down landscape fabric to separate soil from stone, then place a layer of compacted crushed stone to form a solid, flat foundation. Begin with your flattest, widest stones or blocks for the bottom course. Taking time with the first row is critical! If it is level, the rest of the wall will be much easier to build.

Backfilling and Drainage

Backfill after each course of wall stone with 3/4" crushed stone to improve stability and reduce water pressure. Incorporating a perforated drain pipe at the base of taller walls helps water escape and extends the life of the wall.

Accounting for Waste and Settling

Even with precise calculation, you will always need to include some extra material.

Why You Should Order Extra Material

Stone can vary in shape and size, and some will need trimming or cutting. Ordering 5-10% extra ensures you will have enough to finish the project without interruptions. Extra stone can also be useful for future repairs, touch-ups or small landscaping projects.

Common Mistakes to Avoid

Skipping the Base or Using Soil as Backfill

Never install a retaining wall directly onto soil or use excavated soil as backfill. Without sufficient crushed stone and drainage, walls will typically shift and fail over time.

Underestimating Drainage Needs

Water pressure is one of the main causes of retaining wall failure. Always allow for enough crushed stone and drainage piping as required. Failure to install adequate drainage can lessen the lifespan of your wall dramatically.

Final Thoughts and Next Steps

Building a retaining wall takes some forethought and careful workmanship, but if you choose the right stone and install it properly, it can provide a durable, attractive structure for years to come. Use the guidelines above to set your needs, plan your wall, and build with confidence. 

Whether you wish to construct a rustic boulder wall or a neatly stacked block design, if you obtain the necessary stone and preparation, it will make all the difference. And if you are still apprehensive about tackling a retaining wall project, just begin on a small scale - even the smallest wall can change how you enjoy your outdoor living space. Contact Landscape Barn today to get started with the materials and advice you need.

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