To determine how much soil you need, follow these steps:
How to Calculate Soil Volume
- Measure the area : Determine the length and width of the space you want to fill with soil. For irregular shapes, break the area into smaller rectangles, calculate each area, and sum them up.
- Decide the depth : Choose the desired depth of soil. For example, for new gardens or lawns, 2-3 inches is typical; for vegetable gardens, 6-12 inches or more depending on the crop.
- Calculate volume : Multiply the length × width × depth to get the volume. Make sure all measurements are in the same units. If using feet and inches, convert depth inches to feet by dividing by 12.
- Convert to cubic yards or cubic feet :
- To convert cubic feet to cubic yards, divide by 27 (since 1 cubic yard = 27 cubic feet).
- For example, a 3 ft × 6 ft bed with 10 inches (0.83 ft) depth requires 3×6×0.83=153\times 6\times 0.83=153×6×0.83=15 cubic feet of soil, or about 0.56 cubic yards
Soil Volume Examples and Recommendations
- For raised beds, a 3x6 ft bed with 10-inch sides needs about 15 cubic feet of soil, which can be a mix of topsoil, compost, and potting mix
- For lawns, 2-3 inches of topsoil is usually sufficient
- For vegetable gardens, root vegetables like carrots and potatoes need 12-16 inches (300-400 mm) of soil, while other vegetables need 6-8 inches (150-200 mm)
Summary Formula
Soil volume (cubic yards)=Length (ft)×Width (ft)×Depth (inches)324\text{Soil volume (cubic yards)}=\frac{\text{Length (ft)}\times \text{Width (ft)}\times \text{Depth (inches)}}{324}Soil volume (cubic yards)=324Length (ft)×Width (ft)×Depth (inches)
(Where 324 = 27 × 12, converting inches depth to yards)
Additional Tips
- Remove grass or weeds and loosen native soil before filling raised beds to improve drainage and root growth
- Soil settles over time, so consider ordering slightly more than calculated.
- If buying soil in bags, check the volume per bag to determine how many bags you need
By measuring your garden area and desired soil depth, then calculating the volume accordingly, you can accurately estimate how much soil you need for your project.
