How this calculator works
Compost is measured as a layer before incorporation. The new-lawn presets use 1 and 2 inches, consistent with University of Maryland guidance; other depths are planning examples. Use mature compost and a soil test to judge whether more nutrients are needed. Bulk density changes with moisture and screening, so replace the example density with a supplier measurement.
Formula
Volume = area × depth. Mass = volume × bulk density. Depth = volume/area. Area = volume/depth. Bags = ceiling(volume/bag volume). Cost uses the selected CAD per m3, kg or bag basis.
Worked example
A 100 m2 garden covered 2 cm deep needs 2 m3. At a measured density of 500 kg/m3 this weighs 1000 kg. A quote of $50/m3 gives $100 before delivery.
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Frequently asked questions
Are the presets fertilizer recommendations?
No. They only set application thickness. Compost can add substantial phosphorus and salts; use soil testing and local extension advice.
Is the volume before or after settling?
It is the geometric volume at the entered depth. Allow separately for supplier handling, incorporation and settling.
How do I estimate delivery weight?
Multiply volume by measured bulk density. Moisture can change compost weight substantially without changing the order volume.