Mulch Calculator
Use this mulch calculator to turn garden-bed measurements into cubic yards and whole bags to buy. Enter your bed length, width, and finished mulch depth, then adjust the bag size to match your supplier. For a seasonal top-up, enter the existing mulch depth under more options so you only order the extra layer you need.
Mulch to order
1.852cubic yards
- Bed area200 sq ft
- New layer to add3 in
- Volume before allowance1.852 yd³
- Extra allowance (0%)+0 yd³
- Bags (2 cu ft each)25 bags
- Same order volume50 cu ft
Updated .
How much mulch do I need?
Mulch covers an area with a layer of material. Multiply the area by the thickness of the new layer, then convert the resulting volume into the units on your quote:
cubic yards = square feet × added depth in inches ÷ 324
order volume = cubic yards × (1 + allowance ÷ 100)
bags = ceil(order volume × 27 ÷ cubic feet per bag)
The divisor 324 combines two conversions: 12 inches per foot and 27 cubic feet per cubic yard. A bed measuring 108 square feet therefore needs exactly one cubic yard at a new depth of 3 inches. In metric, multiply square meters by centimeters and divide by 100 to get cubic meters; one cubic meter is 1,000 liters.
The calculator adds no extra material by default. If your measurements are approximate or the bed has uneven hollows, you can choose an allowance and see it separately. That allowance increases the shopping volume; it is not a recommendation to spread mulch deeper around plants. Bag counts round up only after the allowance is applied.
Worked example: a 20 × 10 ft bed at 3 inches deep
The default example is a new rectangular bed with no existing mulch and 2-cubic-foot bags. Measure the exposed bed area, excluding a path or other surface you will leave uncovered.
- Area: 20 × 10 = 200 sq ft.
- New depth: 3 − 0 = 3 inches.
- Volume: 200 × 3 ÷ 324 = 1.852 cubic yards, rounded for display.
- Cubic feet: 200 × 3 ÷ 12 = 50 cu ft.
- Bags: 50 ÷ 2 = 25 bags. With 3-cu-ft bags, round 16.67 up to 17 bags.
If the bed already has 1 inch of usable mulch, change that field under more options. The new layer is only 2 inches, needing about 1.235 cubic yards or 17 of the 2-cu-ft bags. Assess the existing depth in several places before using that shortcut; a single thick patch can overstate what remains across the whole bed.
Mulch coverage chart at 2, 3, and 4 inches
These volumes assume a completely new layer and no extra allowance. The 4-inch column is a volume comparison, not a general planting recommendation. Choose a depth suited to your material and plants.
| Bed area (sq ft) | 2 in (yd³) | 3 in (yd³) | 4 in (yd³) | 2-cu-ft bags at 3 in |
|---|---|---|---|---|
| 50 | 0.31 | 0.46 | 0.62 | 7 |
| 100 | 0.62 | 0.93 | 1.23 | 13 |
| 150 | 0.93 | 1.39 | 1.85 | 19 |
| 200 | 1.23 | 1.85 | 2.47 | 25 |
| 300 | 1.85 | 2.78 | 3.70 | 38 |
| 500 | 3.09 | 4.63 | 6.17 | 63 |
| 750 | 4.63 | 6.94 | 9.26 | 94 |
| 1000 | 6.17 | 9.26 | 12.35 | 125 |
One 2-cu-ft bag covers 12 sq ft at 2 inches, 8 sq ft at 3 inches, or 6 sq ft at 4 inches. A 3-cu-ft bag covers 18, 12, or 9 sq ft at those depths. Use the actual volume on the package: bags of equal weight need not contain the same volume.
Measure curved beds and compare bags with bulk delivery
Split a curved border into short rectangles, measure each one, and add their areas. For a round bed, use π × radius². A mulched ring uses π × (outer radius² − inner radius²), keeping both radii in the same units. Put the combined result in the total-area field, which replaces length × width. Beds that need different added depths should be calculated separately, then their volumes combined.
Compare the delivered bulk quote with the total bag price for the same volume. Include the delivery charge, where the driver can unload, and how far you will move the pile. Bags can be carried directly to separate beds and unused sealed bags are easier to store. Bulk material avoids opening many small packages. There is no universal cheaper option without your supplier’s prices and minimum delivery quantity.
Spread the mulch evenly and check depth as you go. University of Maryland Extension advises shallow layers around trees and shrubs and keeping mulch away from bark. The appropriate layer varies by material; compost and fine materials do not necessarily need the same depth as coarse bark. A quantity calculator cannot choose the best mulch for a particular plant.
Frequently asked questions
How many bags of mulch equal one cubic yard?
A cubic yard contains 27 cubic feet. That equals 13.5 bags of 2 cu ft, so buy 14 if you need at least one yard; with 3-cu-ft bags, exactly 9 make a yard. Set the bag-volume field to the label on your product. Buying 14 two-foot bags supplies 28 cubic feet, so the small surplus comes from packaging rather than an added waste percentage.
Should I remove old mulch before calculating a top-up?
Measure what will remain after any removal, then enter that as the existing depth. The calculator subtracts it from your target depth and never produces a negative order. If the remaining layer already meets the target, the result is zero. Do not enter the depth before removing a matted layer if you intend to discard it, because that would understate the replacement volume.
How much area will a yard of mulch cover?
Divide 324 by the new layer depth in inches. One cubic yard covers 162 sq ft at 2 inches, 108 sq ft at 3 inches, or 81 sq ft at 4 inches. These are geometric coverage figures with no allowance for uneven spreading. When topping up, use only the additional depth needed, rather than the total finished depth.
Can I use this mulch estimate for several garden beds?
Yes, if all the beds need the same additional depth. Add their areas and enter the total-area override. If one bed needs a fresh 3-inch layer and another needs a 1-inch top-up, calculate them separately. Add their unrounded volumes before rounding to bags when possible, so you do not buy a separate rounding surplus for every small bed.
Does the mulch volume include settling or delivery losses?
The default is the geometric volume only. You can add a percentage under more options if your supplier recommends an allowance for the product or delivery method. The result shows that addition separately. Do not automatically add the same percentage for every mulch: particle size, moisture, how it is loaded, and the condition of the bed all affect what arrives and how it spreads.
Sources and assumptions
- University of Maryland Extension: Mulching Trees and Shrubs — Material-specific depth guidance and keeping mulch clear of trunks. Volume and bag counts use the dimensional formulas shown above.
These results are planning estimates only — verify quantities with your supplier and local building code before you buy or build. See our terms of use.