Garden Soil Calculator
Calculate the total soil volume needed to fill raised garden planter beds, elevated containers, and potting boxes. Provides precise volumetric totals in cubic feet and cubic yards, plus exact 1/3 ingredient proportions for the legendary Square Foot Gardening "Mel’s Mix".
Long dimension of the garden bed
Short dimension of the garden bed (3–4 ft allows reaching center without stepping on soil)
Target soil depth (6–12 inches for shallow vegetables, 12–18 inches for root crops like carrots)
Total volume in cubic feet (most bagged soil is sold in 1.5 or 2.0 cu ft bags)
How to Use This Calculator
- Measure the length and width of your raised garden bed in feet.
- Enter the soil fill depth in inches (12 inches is standard for versatile root depth).
- Review the total cubic feet and cubic yards needed.
- Follow the 1/3 ingredient breakdown if blending your own high-yield Mel’s Mix.
Formula & Calculation Methodology
Mel Bartholemew’s Square Foot Gardening standard specifies equal thirds by volume of blended compost (for nutrition), peat moss or coconut coir (for moisture retention), and coarse horticultural vermiculite or perlite (for permanent drainage and friability).
Worked Example
Classic 8 ft × 4 ft raised bed filled to 12 inches depth
Small herb planter box: 4 ft × 2 ft at 8 inches depth
Frequently Asked Questions
Can I just fill my raised bed with ordinary backyard dirt?↓
Using native backyard soil in a raised bed is not recommended because it compacts easily into a dense brick when enclosed in a box, restricting root drainage and oxygen circulation. A fluffy, well-draining soil mix is essential.
How many 1.5 cu ft bags of soil do I need for an 8x4 bed?↓
An 8x4 ft bed filled 12 inches deep needs 32 cubic feet of soil, which equals approximately 21 to 22 bags of 1.5 cubic foot potting mix (or 16 bags of 2.0 cu ft soil).
What is the difference between vermiculite and perlite?↓
Both aerate soil, but vermiculite holds both water and nutrients longer, making it superior for vegetables. Perlite (expanded volcanic glass) dries out faster and is better suited for succulents or heavy rain climates.
What is a limitation of raised bed soil calculators?↓
Soil mixes settle 10% to 15% after their initial thorough watering; leave 1–2 inches of clearance below the top of the timber frame when filling.
Related Calculators
Source Citation & Disclaimer
Informational tool only; not licensed tax, legal, or financial advice.