How Much Topsoil for a 12-by-32 Garden?

Total Gardening Square Footage

• To calculate gardening square footage, or area, multiply the length of the rectangular space by the width. In this case, that would be 12 x 32, which equals 384 square feet.

Planting Materials and Topsoil Depth

• The type of vegetation being planted greatly impacts how much topsoil is needed. Topsoil depth for a vegetable garden is 8 to 12 inches.

  Topsoil is sold in cubic feet or cubic yard increments. To get the cubic foot multiplier, first divide the desired depth of the topsoil by 12. This equals a depth range of 0.67 to 1 cubic foot.

Cubic Calculations

• Multiply your surface square footage by your depth to get the total number of cubic feet of soil needed. In this case, 384 x 0.67 = 256 cubic feet for an 8-inch topsoil depth, while 384 x 1 = 384 cubic feet for the 12-inch depth.

  Bulk topsoil is sold in cubic yard increments. To calculate this, divide the total amount of cubic feet by 27, which is the number of cubic feet in a cubic yard. For the 8-inch soil depth, for instance, 256 / 27 = 9.48 cubic yards. For the 12-inch depth, 384 / 27 = 14.22 cubic yards.