Last Updated on October 7, 2022 by Stephanie
Mulch is any organic or inorganic material used to cover your soil to reduce weed growth, control temperature, deter pests and retain moisture for your plants.
As it comes in different forms, how much a cubic foot of mulch weighs depends on which material you plan to use.
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How Much Does 9 Cubic Feet of Mulch Weigh?
Here are approximate weights for 9 cubic foot of commonly used mulches:
9 cubic feet of straw mulch weighs around 180 pounds.
9 cubic feet of compost mulch weighs around 396 pounds.
9 cubic feet of wood mulch weighs around 90 pounds.
Approx. Weight (pounds)
Typical Bag Size
(cubic feet per bag)
(square feet per bag)
1 & 2.5
200 & 500 (laid 1-inch thick)
1 & 2
6 & 12 (laid 2-inches thick)
6-12 (laid 2-4 inches thick)
The approximate weight of stones will be heavier and depend on which type you choose. The weight of rubber or plastic will sit somewhere between organic mulch and rocks.
How Much Will My Mulch Weigh and How Much Do I Need?
The weight will depend on the quantity of mulch you require and the type of material you use.
Because bags of mulch are typically sold in cubic feet, it will help to know what type you plan to use and how many cubic feet youll need. Then you can determine the weight as well as the number of bags you require.
How to Calculate How Many Cubic Feet You Need
To work this out, youll first need to know the width and length of the area you plan to lay mulch and the depth of mulch required. This will give you the cubic feet estimate.
- Square Footage of Area to Mulch: Multiply the width and length of your area together to give you the square feet of the area. For example, I want to mulch 4 feet x 8 feet of garden. 4×8 = 32 square feet. If the shape isnt regular, just measure a rough rectangle around it and use that as a guide. To mulch a circle (e.g., around a tree), take the diameter of the area you will mulch, divide the diameter by 2, then multiply the number by itself. Then multiply that by 3.14.
- Depth of Mulch: Typically, 2 inches of mulch is sufficient. More than 4 inches is not recommended as it can prevent water and oxygen from getting to the roots.
- Calculate Cubic Feet: Simply multiply your square footage by the depth or thickness of the mulch layer to get the cubic feet you need. For example, 32 square feet x 2 inches = 64 cubic feet.
Read on to find out how much your mulch will weigh and the coverage youll get from it.
Approximate Weight and Coverage of Different Types of Mulch
Organic mulch, such as straw or wood, is cheaper, weighs less, and covers more area per bag than heavier inorganic mulch, such as stones or rocks. However, it does have to be replenished more frequently than the inorganic type. Inorganic mulch, such as rocks or plastic, is heavier, harder to work with but also need very little maintenance.
Weight and Coverage of Straw Mulch
Great for seed germination, straw is usually sold in bags of 1 and 2.5 cubic feet. Laying it 1 inch thick will ensure seeds have access to sunlight enough to germinate well.
Approximate Weight: 20 pounds per cubic foot
Approximate Coverage: 200 square feet at 1inch thick
Weight and Coverage of Compost Mulch
Applying compost mulch will help your plants grow faster and provide extra nutrients for more flowers and fruiting. Usually sold in bags of 1 or 2 cubic feet, it can be applied either 1 or 2 inches thick.
Approximate Weight: 44 pounds per cubic foot
Approximate Coverage: 12 square feet at 1 inch thick
Weight and Coverage of Wood Mulch
There are lots of options with wood colours and chip size, treated or untreated for insects, and varying wood types. Coverage of this mulch will be roughly similar, but the weight of the mulch will depend on if it is dry or wet (wet being substantially heavier). It is recommended that you lay this type of mulch 2 to 4 inches thick for effective results.
Approximate Weight: 10 pounds per cubic foot if dry (much heavier if wet)
Approximate Coverage: 12 square feet at 2 inches thick
How to Install Mulch Properly
Make sure you remove any grass growth or weeds from the area you will mulch in advance. This can be done by hand or with weed killer (check timeframe from spray to death of weeds or grass to plan this out well).
Before mulching, water the area well to get the soil underneath moist.
When laying mulch it is advised to protect yourself with face mask, garden gloves and eye protection as required.
How to Install Organic (Straw, Wood, Compost) Mulch
These mulches can be placed straight onto the ground and laid evenly across the required area. Push the mulch a few inches away from the base of your plants to avoid increased risk of disease and pests.
Your mulch may need replacing around the 12 month mark, or sooner if it has significantly broken down before then.
How to Install Inorganic (Rocks, Plastic) Mulch
It is recommended you lay weed cloth over the area you plan to mulch with rocks, pebbles, plastic, rubber or other inorganic material. This will help stop the mulch sinking too much into the ground.
Keep the thickness of the mulch layer at approximately 2 inches if possible, as any higher can prevent moisture from reaching the roots of your plants. When using larger rocks such as river rocks, you may need to spend more time on the placement of smaller versus larger rocks for an even coverage.