Raised Bed Soil Volume Calculator
Calculate how much soil you need to fill a raised garden bed in cubic feet, cubic yards, and 40-litre bags.
How to use this tool
- Enter the inside dimensions of your raised bed in feet.
- Enter the depth of soil you need to fill in inches (10–12 in is standard).
- The calculator returns cubic feet, cubic yards, and the number of 40-litre bags to buy.
Calculate exactly how much soil mix you need before building your raised garden bed.
Formula
Volume (ft³) = length (ft) × width (ft) × (depth (in) ÷ 12)
Volume (yd³) = ft³ ÷ 27
40-litre bags = ceil( ft³ ÷ 1.5 )
(One 40-litre bag ≈ 1.5 ft³ of loose potting or garden soil.)
How it works
This calculator multiplies the bed's footprint by the fill depth (converted from inches to feet) to find the total soil volume, then converts that volume into cubic yards for bulk ordering and into 40-litre bag counts for retail purchasing.
The 1.5 ft³ per 40-litre bag conversion is an approximation; actual fill volume varies with soil density and settling. Buying one extra bag is recommended to account for compaction after watering.
Worked example
Worked example
- Inputs: 4 ft long × 8 ft wide bed, 12-inch fill depth.
- Volume in ft³ = 4 × 8 × (12 ÷ 12) = 4 × 8 × 1 = 32 ft³.
- Volume in yd³ = 32 ÷ 27 ≈ 1.185 yd³.
- Bags needed = ceil(32 ÷ 1.5) = ceil(21.33) = 22 bags.
Volume = 32 ft³ (≈ 1.185 yd³); 40-litre bags needed = 22.
Key terms
- Cubic yard (yd³)
- A unit of volume equal to 27 cubic feet, commonly used when ordering bulk soil, mulch, or gravel from a supplier.
- Fill depth
- The depth of new soil added to the raised bed, measured in inches; may be less than the full bed height if the bed already contains some material.
- 40-litre bag
- A standard retail bag of potting or garden soil; roughly equivalent to 1.5 ft³ of loose material.
- Soil settling
- The compression of loose soil after watering and over time, which reduces the effective volume by 10–20%; buying a little extra accounts for this.
Frequently asked questions
- How much soil do I need for a raised bed?
- Multiply the inside length × width (ft²) by the fill depth in feet (inches ÷ 12). A 4×8 ft bed filled 12 inches deep needs 32 cubic feet of soil.
- What soil mix is best for raised beds?
- A popular recipe is the Mel's Mix: 1/3 compost, 1/3 peat moss or coir, and 1/3 coarse vermiculite. This provides excellent drainage and nutrient retention.