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Last updated: 3 October 2026
Compost calculator
Work out compost for beds, borders and new planting. Australian units: metres, centimetres and litres. Results update as you type.
How to use this calculator
Measure the length and width of the area in metres, then decide how deep you want the compost in centimetres. For odd shapes, split the area into rectangles and add them up using the number of areas box.
A typical depth is about 5 cm as a top dressing, or 5–8 cm to dig in. These are common guidelines, not rules. Follow the advice for your project or product.
How it's calculated
Volume = length × width × depth. Depth is converted to metres (cm ÷ 100). Weight uses a typical density of 0.6 tonnes per cubic metre. Real products vary with moisture and type, so treat weight as a guide.
Worked example
An area 3 m long and 2 m wide, filled 5 cm deep: 3 × 2 × 0.05 = 0.3 m³, about 0.18 tonnes at a typical 0.6 t/m³. That's 10 bags of 30 litres, or about 4 loads in an 85 litre barrow.
Common questions
Should I order extra?
Adding around 10% is sensible. Loose material settles and compacts once it's spread and watered, and uneven ground uses more than a flat measurement suggests.
Is it cheaper to buy in bulk?
For larger areas, usually. Australian landscape suppliers typically sell by the cubic metre, which is often cheaper than bags for big jobs. Compare the price per cubic metre against the bag price.
How much does compost weigh?
We use a typical 0.6 tonnes per cubic metre. Wet material can weigh noticeably more. If weight matters for delivery or a trailer, ask your supplier for their figure.