WeekendCalc

Raised Bed Soil Calculator

Enter your raised bed size and how deep the soil should be. You get the volume to fill it, how many bags to buy, and the amount of each ingredient for a three-part mix.

Your project

beds
%

Fresh soil settles by an inch or two. 10% covers it.

Results

Soil to fill the bed(s)
35.2 ft³
In cubic yards
1.30 yd³

If you buy bags

1 ft³ bags
36 bags
1.5 ft³ bags
24 bags
2 ft³ bags
18 bags

Three-part mix (equal thirds)

Compost
11.7 ft³
Peat moss or coco coir
11.7 ft³
Vermiculite or perlite
11.7 ft³
  • A popular recipe is equal parts compost, peat moss or coco coir, and vermiculite. Other mixes use topsoil and compost, which is cheaper for large beds.

How this calculator works

A raised bed is a box, so the soil volume is length × width × depth. We add an allowance for settling, convert to cubic feet and cubic yards, and show the bag count. The three-part mix simply splits the total into equal thirds.

cubic feet = length × width × (depth ÷ 12) × beds × (1 + settling %)

Worked example: one 4 × 8 ft bed filled 12 in deep is 32 ft³. With a 10% settling allowance you need 35.2 ft³, which is 1.3 yd³ or 18 bags of 2 ft³.

Tips before you buy

  • Fill beds to about an inch below the rim so water does not wash soil over the sides.
  • Bulk soil is far cheaper than bags once you need more than about 20 ft³. A single 4 × 8 ft bed at 12 in is already 1.3 yd³.
  • You can save on fill by stacking logs, branches or leaves in the bottom of deep beds (a "hügelkultur" base), and filling only the top 8 to 12 in with soil mix.
  • Plan on topping up with an inch or two of compost each spring.

Quick answers by size

3 × 3 ft bed9.9 ft³ at 12 in4 × 4 ft bed17.6 ft³ at 12 in3 × 6 ft bed19.8 ft³ at 12 in2 × 8 ft bed17.6 ft³ at 12 in4 × 8 ft bed35.2 ft³ at 12 in4 × 12 ft bed52.8 ft³ at 12 in6 × 6 ft bed39.6 ft³ at 12 in

Tools & materials for this project

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Raised garden bedRaised bed soil mixGarden hose and sprayerVermiculiteDrip irrigation kit

Frequently asked questions

How much soil do I need for a 4x8 raised bed?

A 4 × 8 ft bed filled 12 in deep needs 32 ft³, plus about 10% for settling, so roughly 35 ft³ (1.3 cubic yards).

How deep should raised bed soil be?

Eight to twelve inches is enough for most vegetables. Deep-rooted crops like tomatoes and carrots do better with 12 in or more.

Is it cheaper to buy soil by the bag or in bulk?

Bulk, by a wide margin, once you need more than 20 to 30 ft³. Bagged soil is convenient for one small bed or topping up.

Related calculators & guides

Topsoil CalculatorCubic yards, tons and bags of topsoil, compost or fill.Mulch CalculatorCubic yards or bags of mulch for any bed, with a bulk vs bag cost check.Cubic Yard CalculatorCubic yards, cubic feet and weight for any material.How Much Soil Do I Need for a Raised Garden Bed?Guide

Estimates only. Results assume standard materials and simple shapes. Supplier products vary, and the final call on quantity, structure and safety is yours. Check your local code and your supplier's guidance before ordering.