How much mulch do I need?
Published · Updated · By Sai Nath
Multiply the bed’s area in square metres by the mulch depth in metres. A 12 m² bed at 75 mm needs 12 × 0.075 = 0.9 m³, or 900 litres; at 100 mm it needs 1.2 m³. One cubic metre covers 13.3 m² at 75 mm and 10 m² at 100 mm. Order a little extra, because mulch settles.
In the app: Soil in MeisterCalc, with a worked example and real screens.
Checked on 5 November 2026. Mulch is sold by the cubic metre from landscape yards and by the litre in bags, so the sum is a volume: area times depth. The depths here come from a council’s landscape guideline and a mulch supplier, each linked; the bed you are covering sets the rest.
How do I work out how much mulch I need?
- Measure the bed’s length and width in metres and multiply them for the area in m².
- Pick a depth and turn it into metres: 50 mm = 0.05, 75 mm = 0.075, 100 mm = 0.1.
- Multiply: area × depth = cubic metres of mulch.
- For bags, multiply the cubic metres by 1,000 for litres, then divide by the litres printed on the bag.
Measure the depth you want after spreading, not the depth of the pile. Odd-shaped beds split into rectangles, and each rectangle is added on.
Worked example: an 8 m × 1.5 m garden bed
A bed along a fence, 8 m long and 1.5 m wide.
- Area: 8 × 1.5 = 12 m².
- At 75 mm: 12 × 0.075 = 0.9 m³, which is 900 litres.
- At 100 mm: 12 × 0.1 = 1.2 m³, which is 1,200 litres.
- With 10% on top for settling and spillage: 0.9 × 1.1 = 0.99 m³ at 75 mm.
How deep should mulch be?
Most beds take 75 to 100 mm:
- Hume City Council’s landscape guideline asks for organic mulch “to a depth between 75mm-100mm for garden beds and tree bowls”, 50 mm around remnant trees, and mulch kept away from the trunks of trees and shrubs to avoid rotting (Hume City Council, Landscape Guidelines: Mulch).
- Australian Native Landscapes, a Sydney mulch supplier, says mulch “should be applied to a depth of 100mm” and recommends weed mat underneath if you lay less than that (ANL, garden mulch FAQs).
Thinner layers cover more ground for the same order. Per cubic metre:
| Depth | Mulch per m² | Area 1 m³ covers |
|---|---|---|
| 50 mm | 0.05 m³ (50 L) | 1 ÷ 0.05 = 20 m² |
| 75 mm | 0.075 m³ (75 L) | 1 ÷ 0.075 = 13.3 m² |
| 100 mm | 0.1 m³ (100 L) | 1 ÷ 0.1 = 10 m² |
How many bags of mulch do I need?
Bags are sold by volume, and the litres are on the bag. Divide the litres you need by the bag size and round up.
For the 12 m² bed at 75 mm (900 litres): if your bags say 50 L, that is 900 ÷ 50 = 18 bags; with the 10% extra, 990 ÷ 50 = 19.8, so 20 bags. If they say 30 L, 990 ÷ 30 = 33 bags. Past a cubic metre or so, compare the price of the bags with a bulk load from a landscape yard.
How do I work out mulch for a round bed or a tree ring?
A round bed is π × radius² × depth. A bed 2 m across has a 1 m radius: 3.1416 × 1 × 1 × 0.075 = 0.2356 m³ at 75 mm, about 236 litres.
For a ring around a tree, work out the outer circle and take off the inner one. A ring 2 m across, with the mulch kept back from the trunk inside a 600 mm circle, is 0.2356 − (3.1416 × 0.3 × 0.3 × 0.075) = 0.2356 − 0.0212 = 0.2144 m³ at 75 mm.
In MeisterCalc, Home ▸ Concrete ▸ Holes is a cylinder: enter Diameter 2000 mm, Depth 75 mm and Number of Holes 1 and it shows Total 0.2356 m³; the 600 mm circle at 75 mm shows 0.0212 m³.
How much does a cubic metre of mulch weigh?
It depends on the product and how wet it is, and no single figure fits pine bark, hardwood chip and sugar cane alike, so none is given here. You rarely need the weight: yards sell mulch by the cubic metre. If you need tonnes for a trailer or a ute, ask the supplier for the kg per m³ of that product and multiply: tonnes = m³ × kg per m³ ÷ 1,000. The general method is in cubic metres to tonnes, and trailer loads are in how many cubic metres fit in a trailer.
MeisterCalc’s Soil calculator gives tonnes, but only for the density you type in. Its starting figure, 1,200 kg/m³, is for soil: for the 0.9 m³ bed it shows Weight 1.080 t, which is a soil weight, not a mulch one. Replace it with the supplier’s figure first.
Is bark the same sum?
Yes. Bark chips, wood chip, pebbles used as mulch and sugar cane mulch are all a depth over an area, so area × depth gives the volume for each. Only the weight differs, which is why the yard’s own figure matters if you buy by the tonne. For stone, see how much gravel you need.
Why order more than the calculated figure?
Mulch settles and breaks down; Hume’s guideline sets the finished level to match the edges “after settlement”, so you spread a little proud and it drops. Beds are rarely flat, edges spill, and a bag short means another trip. Ten percent is a sensible start for a flat bed; add more for a sloping or uneven one. The same reasoning is in how much extra concrete to order.
What MeisterCalc does and doesn’t do
- Concrete ▸ Slab and Concrete ▸ Holes give volume in m³ for rectangles and circles; Slab also shows litres. Both are free.
- Soil gives volume and tonnes for the density you enter, with a fixed +10% order row in tonnes.
- There is no mulch preset, no bag counter and no mulch densities. Bag counts are the division above.
- It doesn’t know how deep your plants want their mulch. The supplier and the plant do.
Try it
Concrete, Stairs and Check Square are free to use, with no trial and no card needed. The other 13, Soil and Gravel included, unlock with a one-time purchase, no subscription required, or with a weekly subscription that starts with a 3-day free trial; Google Play shows the prices in your currency. Calculations work offline on Android 7.0 or later.
Sources
- Hume City Council, Landscape Guidelines: Mulch: organic mulch 75–100 mm in garden beds and tree bowls, 50 mm around remnant trees, kept away from trunks, finished levels after settlement. Checked on 5 November 2026.
- Australian Native Landscapes, garden mulch FAQs: 100 mm depth, weed mat under thinner layers. Checked on 5 November 2026.