Core Aeration Calculator

How it works

A core aerator pulls plugs of soil and thatch out of the lawn, leaving a grid of holes. On a grid with holes a inches apart across the machine and b inches apart along its travel, each hole has a × b square inches to itself, so one pass makes 144 ÷ (a × b) holes per square foot; more passes multiply that.

Each hole is a cylinder: its opening is π × (diameter ÷ 2)², and the soil it held is that area times the depth. Holes per square foot times the opening area, over 144 sq in, is the share of the surface opened. Holes times the core volume is the soil brought up, and the same volume of topdressing would fill the holes level.

Extension figures for the machine settings vary. Clemson HGIC 1200 (revised 2020) gives tines of 1/4 to 3/4 in, 2 to 3 in deep and 2 to 3 in apart, with two passes at right angles; Wisconsin A3710 notes piston aerators usually pull 3 in cores and drum units rarely more than 2 in.

Formula

holes per sq ft  = 144 ÷ (spacing across × spacing along) × passes
hole opening     = π × (diameter ÷ 2)²            (sq in)
core volume      = hole opening × depth            (cu in)
surface opened   = holes per sq ft × hole opening ÷ 144
soil removed     = holes per sq ft × area × core volume ÷ 1,728   (cu ft)
topdressing to refill = soil removed

Example

Holes 3 in apart each way make 144 ÷ 9 = 16 holes per square foot per pass; two passes make 32. Over 5,000 sq ft that is 160,000 holes.

A 1/2 in core opens π × 0.25² = 0.196 sq in, so 32 holes open 6.28 sq in of every 144: 4.36% of the surface. At 3 in deep each core holds 0.589 cu in, and the lawn gives up 160,000 × 0.589 = 94,248 cu in, or 54.54 cu ft (2.02 cu yd). Spread over the lawn, that is a layer 0.131 in deep, and the same 54.54 cu ft of topdressing would refill the holes.

Assumptions and limitations

• Holes are taken as clean cylinders of the full diameter and depth, on an even grid. Tines that do not reach full depth in dry or hard soil, or spoon tines that make elongated holes, change the figures; Wisconsin A3710 notes drum units rarely go deeper than 2 in in dry soil.
• Holes from different passes are assumed not to overlap. Where they do, the surface opened and the soil removed are less than shown, so the figures are upper bounds.
• The default spacing, core size, depth and passes are illustrative values within the extension ranges cited above, not settings for a particular machine; the spacing for a given aerator is in its manual.
• Cores contain thatch and roots as well as soil, so the topdressing figure is the volume of the holes, not the weight of soil to buy. Wisconsin A3710 describes topdressing as a thin layer, usually no more than 1/4 to 1/2 in.

Frequently asked questions