Soil, mulch and fill calculator

Work out how much topsoil, mulch, compost, sand or gravel to order to spread a layer, raise the ground or fill holes.

Units:

1. Choose the material

Material Extra for settling and waste (%) Weight of 1 m³ (tonnes)

2. Describe each area

Add one row for each bed, path or hole. For a layer, enter the thickness you want. For a hole or trench, enter its depth. For ground that slopes or is uneven, enter the shallowest and deepest fill and it uses the average.

3. Your order

Price per m³ (optional, $)

Order a bit extra. Soil and mulch settle, edges are never perfectly level, and some gets spilled. The settling allowance above is a typical guide. Suppliers sell by loose volume, and the weight of a cubic metre depends on how wet the material is, so ask your supplier for their figures.

How deep should it be?

Typical depths
Job	Typical depth	Notes
Mulch on garden beds	50 to 100 mm (2 to 4 in)	Keep it 5 to 10 cm (2 to 4 in) away from trunks and stems. Top up yearly.
Topsoil for a new lawn	100 to 150 mm (4 to 6 in)	On top of loosened ground, not on compacted clay.
Topsoil or garden mix for new beds	200 to 300 mm (8 to 12 in)	Dig some into the existing soil so the layers blend.
Vegetable beds and raised beds	300 mm (12 in) or the full height of the bed	Roots of most vegetables go 30 cm down.
Compost top-dressing	10 to 25 mm (0.5 to 1 in)	Thin layers feed the soil without smothering plants.
Top-dressing a lawn	5 to 10 mm (0.2 to 0.4 in)	Use sandy loam and rake it in so the grass shows through.
Gravel or crushed rock path	50 to 75 mm (2 to 3 in) over a compacted base	Fit a weed membrane and an edge to hold it in.
Sand bed under pavers	25 to 30 mm (1 in) over compacted road base	Use coarse bedding sand, not soil.

Raising levels and filling holes

Fill in layers. Add 15 to 20 cm (6 to 8 in) at a time and compact each layer before the next. Fill added in one go settles unevenly.
Use the right fill. Use clean sand or road base under paths and paving. Use topsoil or garden mix only for the top layer where plants will grow.
Do not bury trunks or roots. Piling more than about 5 to 10 cm (2 to 4 in) of soil over the roots of an established tree can harm it. Build a retaining ring (a tree well) instead, or ask an arborist.
Slope away from buildings. Ground next to walls should fall away from the house, about 1 in 20 over the first 2 m (a 5% slope), and keep it below the damp-proof course.
Drainage. Filling can block natural water flow. Check where the water will go in heavy rain.
Allow for settling. Fill with loose soil can drop 10 to 20 percent over a season. Mound it slightly.

Native plants. Many Australian natives (banksias, grevilleas, kangaroo paws and other Proteaceae) are sensitive to phosphorus. Use a low-phosphorus native garden mix and leaf or bark mulch, not manure-rich compost or standard fertilised topsoil.

Typical weights and bag sizes

Approximate figures. Check with your supplier.
Material	Weight per m³	Notes
Topsoil (moist)	1.3 to 1.5 tonnes	Very heavy when wet
Garden mix (soil and compost)	0.9 to 1.2 tonnes	Varies with the mix
Compost	0.5 to 0.7 tonnes
Mulch (bark or woodchip)	0.2 to 0.4 tonnes	Light, but bulky
Sand	1.5 to 1.7 tonnes	Heavier when wet
Gravel or crushed rock	1.4 to 1.7 tonnes

Bag sizes vary by brand, commonly 20 to 40 litres (0.7 to 1.4 cubic feet) for soil and mulch in metric countries, and 1 to 3 cubic feet in the US. The calculator assumes a 30 litre or a 2 cubic foot bag. Quick conversions: 1 m³ = 1.31 cubic yards, 1 yd³ = 0.765 m³, 1 tonne = 1.10 US tons, 1 inch = 25.4 mm.

The blueprint planner also gives a quick estimate for any bed, lawn or path you draw. Select it and look for "Materials needed".

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