How to Calculate How Much Soil You Need for a Raised Garden Bed

One of the most common questions people ask before building a raised garden bed is, “How much soil do I actually need?” Buying too little means extra trips, and buying too much means wasted money and leftover bags. The good news is that the math is simple once you break it down.

Step 1: Measure Your Raised Bed

Start by measuring the inside dimensions of your bed, not the outside.

You’ll need:

• Length (in feet)
• Width (in feet)
• Height or depth of soil (in feet)

If your bed height is in inches, divide by 12 to convert it to feet.

Example:

• Length: 8 feet
• Width: 4 feet
• Height: 12 inches (1 foot)

Step 2: Calculate the Volume

Use this basic formula:

Length × Width × Height = Total cubic feet of soil needed

Using the example above:
8 × 4 × 1 = 32 cubic feet of soil

That means you need 32 cubic feet of soil to fill that raised bed.

Step 3: Convert to Bags or Bulk Soil

Most soil is sold either in bags or by the cubic yard in bulk.

Bagged Soil

Common bag sizes:

• 1 cubic foot
• 1.5 cubic feet
• 2 cubic feet

To figure out how many bags you need:
Total cubic feet ÷ bag size = number of bags

Example:
32 cubic feet ÷ 2 cubic foot bags = 16 bags

Bulk Soil

Bulk soil is usually sold by the cubic yard.

1 cubic yard = 27 cubic feet

To convert:
Total cubic feet ÷ 27 = cubic yards needed

Example:
32 ÷ 27 = 1.19 cubic yards

In this case, you’d want to order about 1.25 cubic yards to allow for settling.

Step 4: Account for Soil Settling

Soil always settles after watering and rain.

Plan for:

• 10–15 percent extra soil
• More settling if soil is loose or compost-heavy

Adding a little extra at the start saves you from having to top off later.

Step 5: Choose the Right Soil Mix

Not all soil is created equal, especially for raised beds.

A good raised bed mix usually includes:

• Topsoil or screened loam
• Compost
• Organic matter for drainage

Avoid using straight garden soil or heavy clay, which can compact and drain poorly.

Step 6: Consider the “Fill Method” for Deep Beds

If your raised bed is deeper than 12–18 inches, you can reduce soil costs by filling the bottom with:

• Clean sticks or branches
• Leaves
• Untreated wood
• Compostable yard waste

This method saves money and improves long-term soil health as materials break down.

Step 7: Double-Check Before You Buy

Before heading to the store or ordering bulk soil:

• Recheck measurements
• Confirm bed depth
• Multiply totals if you have multiple beds

A few minutes of checking can save a lot of hassle later.