How Much Mulch Do I Need? Mulch Calculator & Cubic Metre Guide
- Aug 19
- 8 min read
If you're planning to mulch your garden, one of the first questions you're probably asking is:
How much mulch do I need?
Working out how many cubic metres of mulch to order can seem confusing, especially if you've never purchased landscaping materials in bulk before. But once you know the size of your garden and the depth you want your mulch, the calculation is surprisingly simple.
In this guide, Murray River Mulch explains how to calculate mulch quantities in cubic metres, how much area 1m³ of mulch will cover, what different mulch depths mean, and how to visualise your order before arranging your bulk mulch delivery in Perth.
Quick Answer: How Much Mulch Do I Need?
To calculate how many cubic metres of mulch you need:
Garden area in m² × mulch depth in metres = cubic metres of mulch required.
For example, if you have a 100m² garden and want to spread your mulch 50mm deep:
100m² × 0.05m = 5m³ of mulch
So, you would need approximately 5 cubic metres of mulch.
Quick Mulch Calculator Formula
Measure:
Length × Width = Area in m²
Then:
Area × Depth = Mulch Required in m³
Remember that your mulch depth needs to be converted from millimetres to metres:
25mm = 0.025m
50mm = 0.05m
75mm = 0.075m
100mm = 0.1m
That's it!
How Much Area Does 1 Cubic Metre of Mulch Cover?
The amount of garden that 1 cubic metre of mulch covers depends on how thickly you spread it.
As a general guide:
Mulch Depth | Approximate Coverage From 1m³ |
25mm | 40m² |
50mm | 20m² |
75mm | 13.3m² |
100mm | 10m² |
So, if you're planning to lay your mulch at approximately 50mm deep, 1m³ of mulch will cover around 20m².
If you have a 200m² area at the same depth, you would need approximately 10m³.
What Does 1 Cubic Metre of Mulch Actually Look Like?
Bulk mulch is generally sold by volume rather than weight, which is why you'll see quantities listed in cubic metres (m³).
One cubic metre represents enough material to fill a space measuring:
1 metre long × 1 metre wide × 1 metre high.
But let's be fair — most people aren't standing in their backyard imagining a perfect one-metre cube!
A trailer can provide a much easier visual comparison.
How Many Cubic Metres of Mulch Fit in a 6×4 Trailer?
As a rough visual guide, a standard 6×4 trailer can carry approximately 0.75m³ of mulch, depending on the trailer's actual dimensions, side height and how it is loaded.
Using 0.75m³ as a simple guide:
Bulk Mulch Quantity | Approx. 6×4 Trailer Loads |
0.75m³ | 1 |
1.5m³ | 2 |
3m³ | 4 |
6m³ | 8 |
10.5m³ | 14 |
15m³ | 20 |
Suddenly, a larger mulch order looks a little different!
For example, 10.5m³ of mulch is roughly equivalent in volume to 14 trailer loads using this estimate.
That's a lot of loading, unloading and driving back and forth compared with having your mulch delivered directly to your property.
Important: This is intended as a rough volume comparison only. Trailer dimensions, side heights and load capacities vary, and you should always stay within the legal and safe payload limits of your particular trailer and vehicle.
How Do I Calculate Cubic Metres of Mulch?
Let's look at the calculation in more detail.
Step 1: Measure Your Garden
Measure the length and width in metres of the area you want to mulch.
For example:
10m long × 5m wide = 50m²
Your garden area is therefore approximately 50 square metres.
Step 2: Choose Your Mulch Depth
Next, decide how deep you want your mulch.
For example, if you're aiming for 50mm, convert this to metres:
50mm = 0.05m
Step 3: Calculate Your Mulch Quantity
Multiply the two figures:
50m² × 0.05m = 2.5m³
You would therefore need approximately 2.5 cubic metres of mulch to cover the area at an average depth of 50mm.
Mulch Calculator Examples
Here are a few examples to make calculating your mulch order easier.
50m² Garden at 50mm Deep
50 × 0.05 = 2.5m³
You'll need approximately 2.5m³ of mulch.
100m² Garden at 50mm Deep
100 × 0.05 = 5m³
You'll need approximately 5m³ of mulch.
100m² Garden at 75mm Deep
100 × 0.075 = 7.5m³
You'll need approximately 7.5m³ of mulch.
200m² Garden at 50mm Deep
200 × 0.05 = 10m³
You'll need approximately 10m³ of mulch.
500m² Property at 50mm Deep
500 × 0.05 = 25m³
You'll need approximately 25m³ of mulch.
This is why accurately measuring larger landscaping projects before ordering can make such a difference.
What If My Garden Bed Is an Irregular Shape?
Most gardens aren't perfect squares or rectangles.
The easiest solution is to divide an irregular garden into several smaller sections.
For example:
Section 1:5m × 4m = 20m²
Section 2:8m × 3m = 24m²
Total area:
20m² + 24m² = 44m²
If you're spreading your mulch approximately 50mm deep:
44 × 0.05 = 2.2m³
You would need approximately 2.2m³ of mulch.
For curved garden beds, you don't necessarily need to measure every single curve. Breaking the garden into approximate sections will usually give you a much more practical estimate.
How Deep Should Mulch Be?
The amount of mulch you need is directly affected by how deeply you plan to spread it.
A very thin covering will obviously require less mulch, but it may not provide the results you're looking for.
Mulch can be used to help:
suppress weed growth;
retain moisture in the soil;
protect the soil surface;
regulate soil temperature;
improve the appearance of garden beds; and
gradually add organic material to the soil as suitable organic mulches break down.
The right depth can depend on your garden, existing mulch, plants and the mulch product you're using.
This is also why simply asking “How many square metres does a cubic metre of mulch cover?” doesn't have one universal answer — the intended depth matters.
How Much Mulch Do I Need for Weed Suppression?
If weed suppression is one of your main goals, spreading an extremely thin layer of mulch is unlikely to give you the same results as establishing a more substantial mulch layer.
Mulch helps reduce the amount of sunlight reaching the soil surface, which can make it harder for many weeds to establish.
However, mulch shouldn't be treated as a magic weed remover.
Existing weeds should generally be addressed before mulching, and correct preparation can make a big difference to the finished result.
For more information, read our guide to the biggest mulching mistakes and how to avoid them.
Should I Remove Old Mulch Before Adding New Mulch?
Not always.
If your existing mulch is still in reasonable condition, you may simply need to top it up rather than starting again.
For example, if you're aiming for an overall mulch depth of approximately 75mm and already have a reasonable existing layer, you may only need another 25–50mm of fresh mulch.
Check several locations around the garden before calculating your order because old mulch often breaks down unevenly.
If the old layer has substantially decomposed, that isn't necessarily a bad thing either. Organic mulch breaking down can contribute organic matter back into the soil.
Should I Order Exactly the Amount My Mulch Calculator Says?
Your calculation should be treated as a very useful estimate rather than an exact measurement.
Real gardens aren't perfectly flat, and nobody spreads mulch to precisely the same millimetre depth across an entire property.
Some sections will inevitably be slightly deeper than others.
Irregular garden beds, slopes, existing mulch and uneven ground can all affect the amount required.
If your measurements are approximate, allowing a little extra can help prevent the frustrating situation where you're almost finished and run out of mulch.
Is Buying Bulk Mulch Better Than Buying Bags?
For very small projects, bagged mulch can be convenient.
But for larger garden beds and landscaping projects, the number of bags required can become significant very quickly.
Remember:
1 cubic metre = 1,000 litres.
So:
5m³ = approximately 5,000 litres of mulch
and:
10m³ = approximately 10,000 litres of mulch.
For larger residential gardens, acreage, commercial landscaping and property improvement projects, bulk mulch delivery can remove the need to transport large numbers of bags or make repeated trailer trips.
How Do I Know Which Type of Mulch I Need?
Once you've calculated how much mulch you need, the next question is usually:
Which mulch should I choose?
Different mulch products can suit different budgets, appearances and landscaping applications.
We've created a separate Murray River Mulch Comparison Guide that explains the differences between our mulch products and helps you choose the right option for your project.
When Is the Best Time to Mulch in Perth?
Mulching can be beneficial throughout the year, but seasonal conditions can affect why and when you choose to mulch.
Preparing garden beds before the hotter months, for example, can help protect the soil and reduce moisture loss during hot WA conditions.
If you're planning your next garden project, check out our guide to the best time of year to mulch in Western Australia for a more detailed explanation.
Frequently Asked Questions About Mulch Quantities
How much mulch do I need per square metre?
The answer depends on your desired depth.
At 50mm deep, you need approximately 0.05m³ for every 1m², meaning 1m³ covers approximately 20m².
At 100mm deep, 1m³ covers approximately 10m².
How many square metres does 1m³ of mulch cover?
Approximately:
40m² at 25mm deep
20m² at 50mm deep
13.3m² at 75mm deep
10m² at 100mm deep
How many cubic metres of mulch do I need for 100m²?
For a 100m² area:
25mm deep = 2.5m³
50mm deep = 5m³
75mm deep = 7.5m³
100mm deep = 10m³
How many cubic metres are in a 6×4 trailer?
As a rough visual guide, a standard 6×4 trailer may hold around 0.75m³ of mulch, although actual capacity varies depending on the trailer dimensions, side height and how it is loaded.
Always check the capacity and legal payload limits of your individual trailer before transporting landscaping materials.
How do I calculate mulch for an irregular garden?
Break the garden into several smaller rectangles or approximate sections. Calculate the square metres of each section, add them together and multiply the total area by your desired mulch depth in metres.
Bulk Mulch Delivery Across Perth
Once you've measured your garden, calculated your cubic metres and selected the right mulch, the last thing you want is to spend your weekend making trailer trip after trailer trip.
That's where Murray River Mulch can help.
We supply bulk mulch and landscaping materials from our base in Oldbury, Western Australia, with delivery available throughout a large portion of the Perth region and surrounding areas.
We've also simplified our pricing structure so delivery is already incorporated into our product pricing for Zones 1–3, covering locations within 60km of our Oldbury base.
For customers further away, our extended delivery zones have simple additional delivery fees.
Simply choose your product and quantity, add it to your cart and enter your delivery details at checkout.
Ready to Order Your Mulch?
Before ordering, remember the three simple steps:
1. Measure your area in square metres.2. Decide how deep you want your mulch.3. Multiply the area by the depth in metres to calculate your cubic metres.
And if you're struggling to visualise the amount:
As a rough guide, approximately 0.75m³ of mulch is around one standard 6×4 trailer load.
When you're talking about several cubic metres of mulch, those trailer trips can add up very quickly.
Measure it. Calculate it. Choose your mulch. Then let Murray River Mulch handle the delivery.
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