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Soil calculator

Topsoil, compost and mulch for leveling, lawns, beds, raised beds and trees, how many rounds a lawn needs to level it, and what a drainage test tells you.

Soil calculator

How it is worked out

Loose soil weighs about 1.4 t per m³. A lawn wants about 150 mm of topsoil (see 10.2). Raised beds are filled with ½ to ⅔ topsoil and the rest compost (see 10.5).

A tree hole is 2 to 3 times as wide as the root ball and no deeper than the ball (see 10.3). Topdressing goes on no more than 12 mm at a time (see 10.7).

Drainage: the drop in 15 minutes × 4 is the rate per hour. Under 25 mm per hour drains poorly; 25–75 mm per hour suits most plants; over 100 mm per hour is very free-draining (see 10.6).

Sources

  1. US EPA, Volume-to-weight conversion factors: loose soil or sandy loam: 2,392 lb per cubic yard, about 1.42 t/m³
  2. University of Idaho Extension CIS 1062, Starting a home lawn: topsoil at least 100–150 mm (4–6 in) deep; sandy loam to loam preferred
  3. University of Kentucky AGR-203: ideally 150 mm (6 in) of topsoil; mix the first 50 mm (2 in) into the existing soil to avoid an abrupt change in texture
  4. Clemson University HGIC, Topdressing a home lawn: no more than 12 mm (½ in) at a time; light and frequent applications; sand only where the native soil is sandy
  5. University of Minnesota Extension, Raised bed gardens: ½ to ⅔ topsoil and ½ to ⅓ plant-based compost; potting soil dries out too quickly; avoid old CCA-treated wood and railroad ties
  6. Utah State University Extension, Tree planting rules: hole at least 3 × the root ball; backfill with native soil, no amendments; root collar at or just above the soil
  7. University of Illinois Extension, Proper mulching techniques: mulch 2–4 in (50–100 mm) deep, compost 2–3 in, coarse mulch 3–4 in; keep mulch at least 4 in (100 mm) away from the trunk
  8. Minnesota Pollution Control Agency, Minnesota Stormwater Manual: tree soil volume: 2 ft³ of rootable soil per ft² of mature canopy (about 0.6 m³ per m²); Toronto 30 m³ and Langley 10 m³ per tree
  9. Iowa State University Extension, Testing and improving soil drainage: hole at least 300 mm deep, 100–300 mm wide; fill, drain, refill, measure 15 minutes × 4; under 25 mm/h poor, 25–75 mm/h desirable, over 100 mm/h very well drained
  10. University of Illinois Extension, Improving soil drainage (2022): same procedure and rates; do not test when the soil is very wet
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