Topdressing Calculator

The formula converts area and depth into cubic yards:

cu yd = area (sq ft) x depth (inches) / 324

324 = 12 (inches per foot) x 27 (cu ft per cu yd)

Equivalently: cu yd = area x depth x 0.003086   (1/324 exactly)

Per 1,000 sq ft:  cu yd = 1,000 x depth / 324
  1/8 in:  0.386 cu yd per 1,000 sq ft
  1/4 in:  0.772 cu yd per 1,000 sq ft
  3/8 in:  1.157 cu yd per 1,000 sq ft
  1/2 in:  1.543 cu yd per 1,000 sq ft

bags   = ceil(cu yd x 27 / bag size in cu ft)
hopper loads = ceil(cu yd / hopper capacity in cu yd)

Worked example: 5,000 sq ft at 1/4 inch depth = 5,000 x 0.25 / 324 = 3.86 cu yd (104.2 cu ft). At 1.0 cu ft bags, that is 105 bags. At a 1.5 cu yd hopper, that is 3 loads.

The 1/324 conversion (rounded to "x 0.0031") comes from first principles: 1 cu yd = 27 cu ft = 27 x 1,728 cu in = 46,656 cu in. The Virginia Cooperative Extension (VCE) publishes the rounded form: "Area to cover (square feet) X depth of compost (inches) X 0.0031 = compost needed (cubic yards)" (PWC VCE, "Composting the Lawn" PDF, pwcva.gov, fetched 2026-10-24). The VCE also recommends spreading compost "to about ¼ inch thick" and warns "don't apply it much thicker ... because that can smother your grass."

Topdressing and the topsoil calculator share the same cu-yd-from-depth math, but they solve different problems. The topsoil and soil calculator has depth presets starting at 1 in with a settling buffer for grade fill, and outputs bulk tons and a bulk-vs-bagged cost comparison. This page works at fractional-inch depths (1/8 to 1/2 in), outputs per-1,000 sq ft volume (the way topdresser operators think), and adds hopper loads for the equipment step that topsoil jobs do not have.