Soil for a 15-Inch Deep Raised Bed
A 15-inch deep raised bed gives you extra depth for tomatoes, peppers, and moderately deep-rooted vegetables while not quite requiring as much soil as a full 18-inch bed. For a 4×8 bed at 15 inches, you'd need 40 cubic feet of soil. Enter your dimensions in the calculator and use 15 inches as your depth to get your exact volume and bag count.
How to Use This Calculator
Select your bed shape (Rectangle, Square, or Circle), choose your unit of measurement, then enter your dimensions. For rectangular and square beds, enter length, width, and depth. For circular beds, enter the diameter and depth. Click Calculate Soil Needed to see your results instantly in cubic feet, cubic yards, liters, and gallons — plus bag counts for all four standard bag sizes.
Understanding Your Results
Cubic feet is the unit printed on most bagged soil at garden centers. Use this number to count bags. Cubic yards is the unit used by landscape bulk suppliers — divide cubic feet by 27 to get cubic yards. Liters is the metric equivalent (1 cu ft = 28.32 liters). Gallons is helpful for smaller container calculations (1 cu ft = 7.48 gallons).
Soil Mix Recommendation
The best all-purpose raised bed mix is 60% quality topsoil, 30% compost, and 10% perlite or coarse sand. This blend drains well, retains moisture, and provides the nutrients plants need. Avoid filling raised beds with pure topsoil — it compacts and restricts root growth. Always include at least 25–30% organic matter.