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Raised Bed Soil at 12-Inch Depth

Twelve inches is the most popular raised garden bed depth. It suits nearly every vegetable, is affordable to fill, and provides excellent drainage. A 4x4 at 12 inches needs 16 cubi…

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Raised Bed Soil at 12-Inch Depth

Twelve inches is the most popular raised garden bed depth. It suits nearly every vegetable, is affordable to fill, and provides excellent drainage. A 4x4 at 12 inches needs 16 cubic feet; a 4x8 needs 32 cubic feet; a 4x12 needs 48 cubic feet. Enter your bed dimensions in the calculator above and set depth to 12 inches to get your exact soil requirement.

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).

Volume Formula (Rectangle)
Volume = Length × Width × Depth (all in feet)

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.

💡 Order 10% extra: Soil settles 10–15% after the first thorough watering. Buying a little extra prevents a second trip to the store.
Common Questions

Frequently Asked Questions

A 4×8 foot raised bed at the standard 12-inch depth requires 32 cubic feet of soil — about 1.19 cubic yards. You would need 32 one-cubic-foot bags or 16 two-cubic-foot bags. At an 18-inch depth you need 48 cubic feet, and at 24 inches you need 64 cubic feet. Use the calculator above to adjust for your specific depth.
The most versatile depth is 12 inches, which suits most vegetables and flowers. For deep-rooted plants like tomatoes and carrots, 18–24 inches is better. For shallow-rooted herbs and lettuce, 6–8 inches is enough. When in doubt, build to 12 inches — it is the best all-purpose choice.
The best all-purpose raised bed mix is: 60% topsoil, 30% compost, 10% perlite or coarse sand. For a premium option, try Mel's Mix: equal thirds of compost, peat moss (or coco coir), and coarse vermiculite. Avoid filling beds with pure topsoil — it compacts and drains poorly in a raised environment.
Tomatoes need a minimum of 12 inches of soil, but they produce the best yields in 18–24 inches of rich, well-draining growing medium. Deeper soil lets roots access more water and nutrients during hot weather and reduces the risk of blossom-end rot caused by inconsistent moisture levels.
One cubic yard contains 27 cubic feet of soil. If you are ordering bulk soil by the yard, use the cubic yard result from the calculator and round up to the nearest quarter or half yard. A 4×8 bed at 12 inches (32 cubic feet) requires about 1.2 cubic yards — so order 1.5 cubic yards to have a comfortable margin.
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