Mulch Calculator
Find out how many cubic yards or bags of mulch you need. Enter the size of the bed and how deep you want the mulch, and the calculator counts the bags for you.
How to use the calculator
- Measure the length and width of each bed. For a round bed, measure across the middle.
- Enter the depth. See the guide below if you are not sure.
- Choose your bag size, which is printed on the bag. Skip it if you are buying in bulk.
- Add a price per bag or per cubic yard if you want a cost estimate.
How the calculation works
- Volume = length × width × depth, with depth converted from inches to feet.
- With extra = volume × (1 + extra percent ÷ 100).
- Cubic yards = cubic feet ÷ 27.
- Bags = cubic feet ÷ bag size, rounded up to a whole bag.
Worked example
A garden bed 20 ft long and 5 ft wide, mulched 3 inches deep, with 5 percent extra.
- Area: 20 × 5 = 100 sq ft
- Volume: 100 × (3 ÷ 12) = 25.00 cu ft
- With 5 percent extra: 26.25 cu ft, which is 0.97 cu yd
- Bags of 2 cu ft: 26.25 ÷ 2 = 13.12, so buy 14
- Bags of 3 cu ft: 26.25 ÷ 3 = 8.75, so buy 9
How far a bag goes
This shows how much ground each size covers at common depths, before any extra allowance.
| Depth | 2 cu ft bag | 3 cu ft bag | 1 cubic yard |
|---|---|---|---|
| 2 inches | 12 sq ft | 18 sq ft | 162 sq ft |
| 3 inches | 8 sq ft | 12 sq ft | 108 sq ft |
| 4 inches | 6 sq ft | 9 sq ft | 81 sq ft |
How deep to mulch
University extension guides, including those from the University of Illinois and the University of Tennessee, suggest roughly these depths:
| Mulch type | Typical depth |
|---|---|
| Fine mulch (such as shredded or chipped) | 2 to 3 inches |
| Coarse mulch (such as large bark chunks) | 3 to 4 inches |
Around trees, spread mulch out toward the edge of the branches and keep it back from the trunk instead of piling it against the bark. Mulch heaped up the trunk in a cone, often called volcano mulching, can harm the tree.
Bags or bulk
Bagged mulch is easy to carry and store, and suits small beds. Bulk mulch is delivered by the cubic yard and is usually the better fit for larger areas, though delivery fees and minimum loads can change that. Work out the quantity once, then compare both quotes.
Questions
How many bags of mulch are in a cubic yard?
A cubic yard is 27 cubic feet. That is 13.5 bags of 2 cubic feet, or 9 bags of 3 cubic feet. In practice you buy whole bags, so round up.
How deep should mulch be?
Extension services commonly suggest 2 to 3 inches for fine mulch and 3 to 4 inches for coarse mulch. Going deeper does not help and can hold too much moisture around roots.
I am topping up old mulch. How much do I need?
Measure what is already there, then add only enough to bring the total back to the depth you want. Piling new mulch on top of a thick old layer can take the total past the recommended depth.
How do I measure a curved bed?
Split it into rectangles and circles and use Add another area for each one. A rough fit is fine, since you are also adding an allowance for settling. If you know the area already, choose I know the area.
Why does the calculator not show weight?
Mulch weight changes a lot with the type and how wet it is, so a single figure would mislead. The calculator gives volume in cubic yards and a bag count, which are what mulch is sold by.
Is bulk mulch cheaper than bags?
For larger jobs it often is, but delivery fees and minimum loads matter. Put the quotes side by side: enter a price per bag or per cubic yard and compare the estimated cost.