How to Figure Soil Volume for Raised Beds

When building raised flower beds or vegetable gardens, you need to know the total volume of soil that will fill the planting area. Gardening supply centers sell soil and mulch by the cubic foot or cubic yard, so you need to convert the final volume measurements to one of these units. You can use the formulas below or the convenient soil volume calculator.

First, measure the bed's depth, width, and length in inches. Remember that 1 foot is equal to 12 inches. For example, suppose you have a bed that is 8 inches deep, 3 feet wide, and 16 feet long. Then the measurements are

D = 8, W = 36, L = 192.

Next, multiply the three measures to obtain the cubic inches of soil. Using the same example, a bed that is 8 by 36 by 192 has a volume of 55296 cubic inches.

Divide this figure by 1728 to obtain the number of cubic feet. For this example, the volume is 32 cubic feet.

Finally, divide the resulting number by 9 to obtain the cubic yardage. For this example, the volume is 3.556 cubic yards.

The formulas are:

Cubic feet = LWD/1728
Cubic yards = LWD/46656

where L, W, and D are in inches.

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