RUBBER MULCH
How much rubber mulch do I need?
Rubber mulch is the one mulch product where the label on the bag and the way it is sold pull in opposite directions: the bag states a volume in cubic feet, but the pallet is priced and shipped by weight. You need the volume to answer the question, so start there.
The two numbers you need
cubic feet = square feet × depth in inches ÷ 12, then cubic yards = cubic feet ÷ 27.
Then bags: bags = ceiling(cubic feet ÷ bag cubic feet). That last step is why rubber mulch causes more ordering mistakes than wood mulch — rubber bags are sold at 0.8, 1.25, 1.5 and 2 cubic feet, and the bag count for the same bed changes with every one of them.
Worked example, 200 sq ft at 2 inches
Volume first: 200 × 2 ÷ 12 = 33.33 cubic feet, which is 33.33 ÷ 27 = 1.23 cubic yards. Now the bag count by bag size:
| Bag size | Exact bags | Bags to buy |
|---|---|---|
| 0.8 cu ft | 41.7 | 42 |
| 1.25 cu ft | 26.7 | 27 |
| 1.5 cu ft | 22.2 | 23 |
| 2 cu ft | 16.7 | 17 |
Forty-two bags or seventeen, for the same bed. Nothing about the bed changed — only the bag the seller happens to stock.
How deep should rubber mulch go?
In a garden bed, 2 to 4 inches is the working range published by Cornell University's weed management guidance, and N.C. Cooperative Extension puts the figure at 2 to 3 inches over the root zone. Rubber does not decompose, so you are not topping it up every spring the way you would with bark — you install it once at depth.
Playground use is different and is not a gardening decision. The CPSC Public Playground Safety Handbook (Publication 325) sets a 6-inch minimum for shredded or recycled rubber, with every other loose-fill material at 9 inches or more, and it states that loose-fill must be maintained so the level never drops below that minimum.
What the weight figure is for
The 450 to 850 lb per cubic yard range published by the University of Regina's Math Central describes organic mulch. Rubber is denser and that range does not apply to it. If you need to know what a rubber pallet weighs for transport, use the weight the seller publishes for that product rather than a mulch average — the pallet is the shipping unit and the seller has weighed it.
Ordering check before you buy
- Confirm the bag volume printed on the product, not the bag count on the listing.
- Confirm whether the price is for a pallet or for single bags; convert both to price per cubic foot before comparing.
- For a playground, confirm the product's own test data supports your equipment's fall height at the depth you are ordering.
The rubber mulch calculator returns cubic yards and bag counts for all four bag sizes at once.
Related reading: Playground mulch depth — the CPSC depth rule, quoted.