How the calculation works
Volume in cubic metres = length × width × depth in metres. Multiply by 1,000 for litres, add your allowance and round up to whole bags using the product’s stated litre volume. This assumes a level rectangular area.
Worked example
Example: a 4 m × 2 m bed covered 5 cm deep takes 0.40 m³, or 400 L before allowance. Adding 10% gives 440 L; for 50 L bags, round up to 9 bags.
Before you order
Different mulch products settle and vary in particle size. Confirm the recommended depth for your plants and keep mulch clear of stems and tree trunks. Measure irregular beds as smaller sections and add their results.
Questions about this estimate
Is a 50-litre bag always 50 litres of coverage?
Nominal bag volume is the starting point. Loose bark can settle or spread unevenly; use an allowance and check the supplier description.
Can I use this for compost?
You can estimate volume, but compost fill depth and settlement requirements differ from a decorative mulch layer.