Calculate soil and mulch from the finished layer depth

Landscape materials are often priced by cubic metre, bag or tonne. Establish the required layer volume before converting it into the supplier's unit, and identify whether the specified depth describes loose placement or the finished condition.

Convert the depth before multiplying

An illustrative bed 6 m long and 2 m wide, covered 75 mm deep, needs 6 × 2 × 0.075 = 0.9 m³ geometrically. That is 900 L. If the chosen product is sold in 50 L bags on the same volume basis, the starting count is 18 bags before any selected allowance.

Subtract occupied volumes carefully

A raised bed's external dimensions may include its walls. Use the internal fill dimensions, then account for any separately specified drainage or other layers. Existing soil, root balls or structures should be deducted only when their displacement is relevant and reasonably measured.

Do not guess a tonne conversion

At an illustrative supplied density of 1.3 t/m³, 0.9 m³ corresponds to 1.17 t. That density is an example, not a general value for soil or mulch. Moisture and material composition can change mass, so confirm the supplier's basis.

Keep settlement separate

A delivery allowance may be needed for the selected material and placement method, but it should have a stated basis. Increasing finished depth and then applying another allowance for the same settlement can overstate the order. Record footprint, target depth, material condition and purchase unit on the enquiry.

Found a measurement or calculation issue? Send the example and your correction.