A mulch calculator tells you how many cubic yards of mulch you need for a garden bed from its length, width and depth. A 10 × 10 ft bed at 3 inches needs about 0.93 cubic yards, or 13 two-cubic-foot bags.
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How to use the mulch calculator
- Enter the bed length in feet.
- Enter the bed width in feet.
- Enter the depth in inches, usually 2 to 3.
- Read the cubic yards; multiply by 27 for cubic feet.
How the mulch calculator works
The mulch calculator multiplies the length and width of a bed in feet by the depth converted to feet (inches ÷ 12). That gives cubic feet. Dividing by 27, the number of cubic feet in a cubic yard, gives the cubic yards that bulk suppliers sell. All three measurements must be greater than zero. A shortcut used by extension services gives the same answer: square feet × depth in inches ÷ 324 = cubic yards.
Mulch calculator worked example
A 10 × 10 ft bed covered 3 inches deep needs 10 × 10 × 0.25 = 25 cubic feet. The mulch calculator divides by 27 and shows 0.926 cubic yards. If you buy bags, divide the cubic feet by the bag size: 25 ÷ 2 = 12.5, so buy 13 bags of 2 cubic feet. A 30 × 10 ft bed at the same depth needs 2.778 cubic yards, which most suppliers would round to 3.
| Bed | Depth | Cubic yards | Cubic feet | 2 ft³ bags |
|---|---|---|---|---|
| 10 × 10 ft | 3 in | 0.926 | 25.0 | 13 |
| 20 × 5 ft | 2 in | 0.617 | 16.7 | 9 |
| 30 × 10 ft | 3 in | 2.778 | 75.0 | 38 |
| 12 × 4 ft | 4 in | 0.593 | 16.0 | 8 |
| 50 × 20 ft | 2 in | 6.173 | 166.7 | 84 |
How deep to spread mulch
Clemson Cooperative Extension recommends a layer of two to three inches in plant beds and around trees and shrubs. That depth helps hold moisture, moderate soil temperature, reduce erosion and suppress weeds. Finer mulches can mat and shed water if piled deeper, while coarse bark nuggets let more air through. More is not better: deep mulch can starve roots of air. Keep mulch a few inches away from tree trunks and plant stems, and avoid building a cone, sometimes called a mulch volcano, around a tree.
Measuring odd shapes
The tool expects a rectangle. For a circle, such as a ring around a tree, find the area as 3.14 × radius × radius and enter that area as the length with a width of 1. For an irregular bed, split it into rectangles and add the results, or measure the longest length and the average width. For a triangle, enter the base and half the height. Round up a little to allow for settling and uneven ground.
Topping up an existing bed
Organic mulches such as shredded bark and wood chips break down over a season or two, which adds organic matter to the soil. If an inch remains from last year, you only need to add an inch or two. Measure the depth that is left in a few spots and enter the difference as the depth in the mulch calculator, so you do not overbuy.
Bulk or bagged mulch
Bags are convenient for small beds and easy to carry. For larger areas, bulk delivery by the cubic yard is usually cheaper per cubic foot, though there may be a delivery fee and a minimum order. One cubic yard is 27 cubic feet, roughly 13 or 14 bags of 2 cubic feet or 9 bags of 3 cubic feet. One cubic yard spread 3 inches deep covers about 108 square feet, and spread 2 inches deep it covers about 162 square feet.
Tips
- Measure in feet and enter the depth in inches.
- Water the bed and pull weeds before spreading.
- Ask your supplier whether a cubic yard is measured loose or settled.
- Use the same formula for compost or topsoil; for stone, a gravel tool adds weight.
Run the mulch calculator for each bed separately, add the totals, then round up to the nearest half yard or whole bag when you order.
General gardening guidance only. Local extension offices can advise on mulch types and depths for your climate and plants.
Related converters and calculators
Related calculators:
- Gravel calculator: stone
- Concrete calculator: slabs
- Square footage calculator: area
- Volume calculator: volume
Sources
Clemson Cooperative Extension: Mulch matters; Iowa State University Extension: How to determine the amount of mulch needed.
Formula and method
Cubic yards = (length_ft x width_ft x (depth_in / 12)) / 27.
Rectangular bed volume converted from cubic feet to cubic yards. Depth is inches.
Questions about this calculator
How much does one cubic yard of mulch cover?
About 108 square feet at 3 inches deep, or 162 square feet at 2 inches.
How deep should mulch be?
Usually two to three inches.
How many bags are in a cubic yard?
About 13.5 bags of 2 cubic feet or 9 bags of 3 cubic feet.
What is the formula?
Square feet × depth in inches ÷ 324 = cubic yards.
Can I use it for a circle?
Yes, enter the circle area as length and 1 as width.
Check the assumptions and units before relying on a result. Financial, tax and health estimates do not replace advice for your individual circumstances.
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