Mulch Calculator (Australia)
A 5 m × 3 m bed 75 mm deep needs about 1.125 m³ (1,125 L) of mulch, or 23 bags of 50 L.
Updated · Australian units: metres, millimetres, cubic metres · Built and checked by AI, which can make mistakes
Work out how much mulch you need
Result
This is an estimate. Real quantities depend on uneven ground, settling, compaction and the exact product, and bag sizes and weights vary by brand. Check the bag or ask your supplier before you buy.
Built and checked by AI. AI wrote this calculator and its explanations, researched the rates and ran the tests. AI can make mistakes, and the checks may not catch them all, so confirm anything important with an official source or a qualified professional. How we use AI.
Quick answer
A 5 m × 3 m bed 75 mm deep needs about 1.125 m³ (1,125 L) of mulch, or 23 bags of 50 L.
Working in feet and inches? Use our US mulch calculator.
How to use the mulch calculator
- Choose the shape of the area: a rectangle, a circle, or enter the area if you already know it.
- Enter the measurements in metres and the depth in millimetres.
- Pick the bag size you plan to buy.
- Optionally open “Compare costs” to see whether bags or bulk is cheaper.
- Press Calculate to see how much you need, with the steps.
How it’s calculated
Area = length × width (m²), or π × (diameter ÷ 2)² for a circle
Volume (m³) = area (m²) × depth (mm) ÷ 1,000
Litres = m³ × 1,000
Bags = litres ÷ litres per bag, rounded up
Worked example
Mulch for a 5 m × 3 m area at 75 mm
- Area: 5 m × 3 m = 15 m².
- Volume: 15 m² × 75 mm ÷ 1,000 = 1.125 m³.
- In litres: 1.125 m³ × 1,000 = 1,125 L.
- Bags: 1,125 L ÷ 50 L per bag = 22.5, rounded up to 23 bags.
How deep should mulch be?
Landscape guidelines from Hume City Council in Victoria call for 75 to 100 mm of organic mulch on garden beds. Thinner layers break down faster and let weeds through.
Keep mulch away from tree trunks and plant stems to avoid rot.
When you’d actually use a mulch calculator
- Topping up garden beds before summer. Work out how many bags to grab before you head to the hardware store.
- Deciding between bags and bulk. Compare the cost of bags with a delivered load.
- Mulching around new trees. Use the circle option for the ring around each trunk.
What this calculator doesn’t include
- Irregular shapes. Split the area into rectangles and circles and add the results.
- Settling and compaction. Organic materials settle after watering, so you may need a little more.
- Delivery fees, minimum orders and local prices, which vary by supplier.
How we calculate
Area comes from your measurements. Volume is area × depth ÷ 1,000, in cubic metres. We calculate at full precision and round only for display. Bag counts are rounded up to whole bags.
Sources:
Frequently asked questions
How many bags of mulch are in a cubic metre?
There are 1,000 litres in a cubic metre, so it takes 20 bags of 50 L mulch, or 25 bags of 40 L, to make a cubic metre.
How deep should mulch be?
Hume City Council’s landscape guidelines call for 75 to 100 mm of organic mulch on garden beds. Keep it away from trunks and stems.
How much area does a bag of mulch cover?
A 50 L bag covers about 0.67 m² at 75 mm deep, or 0.5 m² at 100 mm.