Enter the length and width of your bed, the depth you want and the bag size. You get the volume in cubic yards (or cubic metres) and the number of bags to buy. If you are ordering a bulk delivery, the cubic yard figure is the one to give the supplier.
This calculator needs JavaScript. The formula and a worked example are below.
How to use the mulch calculator
Measure the bed at its longest and widest points. For a curved bed, a rough rectangle that covers the same area is close enough. Enter the depth you want to spread. Check the bag for its size in cubic feet or litres.
If you want a cost, add the price per bag. The estimate uses whole bags, since that is how they are sold.
The formula
Volume (cu ft) = length × width × depth in inches ÷ 12. Cubic yards = cubic feet ÷ 27. Bags = cubic feet ÷ bag size, rounded up.
Worked example
A bed is 20 ft long and 4 ft wide, and you want 3 inches of mulch. The volume is 20 × 4 × 3 ÷ 12 = 20 cu ft, which is 0.74 cu yd. With 2 cu ft bags you need 10 bags.
Bags or bulk?
For a small bed, bags are easy to carry and store. For larger areas, a bulk delivery is usually measured in cubic yards, so use the cubic yard figure above. Read mulch delivery and installation to see how to prepare for the drop-off.
Common mistakes
The usual error is mixing units, such as a depth in inches with a bed in feet, without converting. The calculator does that conversion for you. Another is forgetting that mulch settles, so a bed filled exactly to the line may look thin after a few weeks.
Frequently asked questions
How deep should mulch be?
It depends on the bed and the material. Check the supplier’s guidance for your mulch type, and avoid piling it against plant stems or tree trunks.
How much does a cubic yard cover?
A cubic yard is 27 cu ft. Divide that by the depth in feet to see the area it covers. At 3 inches (0.25 ft) it covers 108 sq ft.
Can I use this for topsoil or gravel?
The volume part works for any loose material. Bag sizes and weights differ, so check the product.
Related guides
Read mulch delivery and installation. For a nearby hard-surface project, try the concrete calculator.