Mulch Calculator
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Result
Mulch needed
- Bags to buy
- 15 × 2 cu ft bags
- Area covered
- 120 sq ft
- In cubic feet
- 30 cu ft
- Cost if bagged
- $67.50
- Cost if bulk
- $42.22
- Bulk saves
- $25.28
- At 1.11 cubic yards, bulk delivery works out about $25 cheaper than 15 bags — before any delivery fee, which is usually the deciding factor on a small order.
Recommended depth by purpose
Mulch depth is a decision rather than a constant. These are the usual choices.
| Purpose | Depth | Why |
|---|---|---|
| Weed suppression | 3–4 in | Below 3 in, light reaches weed seeds |
| Moisture retention | 2–3 in | Enough to shade the soil surface |
| Around trees | 2–4 in | Keep it off the trunk — no volcano mulching |
| Annual top-up | 1–2 in | Refreshing colour over existing mulch |
| Playground safety surface | 9–12 in | Fall attenuation, engineered chips only |
What one cubic yard covers
A cubic yard is 27 cubic feet, so coverage falls as depth rises.
| Depth | Coverage per cubic yard | Equivalent bags |
|---|---|---|
| 1 in | 324 sq ft | 14 |
| 2 in | 162 sq ft | 14 |
| 3 in | 108 sq ft | 14 |
| 4 in | 81 sq ft | 14 |
| 6 in | 54 sq ft | 14 |
How much mulch do I need?
To work out how much mulch you need, multiply the bed's length by its width for the area in square feet, multiply by the depth in feet, then divide by 27 for cubic yards. A 20 by 6 foot bed at 3 inches deep needs 1.11 cubic yards.
cubic yards = (area_sqft × depth_in ÷ 12) ÷ 27 bags = cubic feet ÷ 2- area
- Bed area in square feet
- depth
- Mulch depth in inches, divided by 12 to reach feet
- 27
- Cubic feet in a cubic yard — how bulk mulch is sold
- 2
- Cubic feet in a standard US bag
Mulch is a volume problem: an area multiplied by a depth. The arithmetic is simple and the judgement is in the depth, which is why this page leads with the depth table rather than a single default. Three inches suppresses most weeds by denying seeds light; two inches retains moisture but lets weeds through; above four inches you start holding water against stems and starving shallow roots of air. A cubic yard covers 108 square feet at 3 inches and only 81 at 4, so the depth decision moves the order quantity by a third. The bag-versus-bulk crossover matters more than the volume. One cubic yard is 13.5 standard bags, and bagged mulch typically costs two to three times as much per cubic foot — but bulk carries a delivery fee that can erase the saving on anything under about two yards.
- Measure the bed's length and width in feet.
- Multiply them for the area in square feet.
- Choose a depth — three inches suits most beds.
- Divide the depth in inches by twelve to get feet.
- Multiply area by depth, then divide by 27 for cubic yards.
Worked example: A 20 ft by 6 ft border at 3 inches deep
A 20 ft by 6 ft border at 3 inches deep
The bed is 20 × 6 = 120 square feet. Three inches is 3 ÷ 12 = 0.25 feet, so the volume is 120 × 0.25 = 30 cubic feet. Divided by 27 that is 1.11 cubic yards. In bags, 30 cubic feet at 2 cubic feet each is 15 bags. At $4.50 a bag that is $67.50; the same 1.11 yards in bulk at $38 a yard is $42.22, so bulk saves about $25 before delivery. If the supplier charges $50 to deliver, bags win on this job — the crossover is usually around two yards. Dropping to a 2-inch depth would need only 20 cubic feet, or 10 bags, while going to 4 inches pushes it to 40 cubic feet and 20 bags. That one-inch decision changes the order by a third either way.
What each mulch input means
- Bed shape
- The shape of the area you are covering. A tree ring is a circle with the trunk area removed.
- Length
- The longer side of the bed, in feet. Pace it out if you have no tape — a stride is roughly 2.5 ft.
- Width
- The shorter side, in feet. For an irregular bed, use the average width.
- Outer diameter
- For a circular bed or tree ring, the full width across, in feet.
- Trunk or inner diameter
- For a tree ring, the width of the area left bare around the trunk. Mulch piled against bark rots it.
- Depth
- In inches. Three inches is the usual choice: enough to suppress weeds, not enough to suffocate roots. The table below gives depths by purpose.
- Price per bag
- What a 2 cubic foot bag costs locally, for the bulk-versus-bagged comparison.
- Price per cubic yard
- Delivered bulk price per cubic yard, excluding any delivery fee.
What this mulch does not account for
- Existing mulch is not deducted. Most beds need a 1–2 inch annual top-up rather than a full 3 inches, so measure what is already there and subtract it.
- Mulch settles and decomposes. Bark loses roughly a quarter of its depth in the first year, which is why topping up is an annual job rather than a one-off.
- Irregular beds need splitting into rectangles and circles, or an average width. A curved border measured at its widest point will over-order substantially.
- Bulk delivery fees are not included in the comparison and frequently decide it. Ask for the delivered price, not the per-yard price.
- Bag sizes vary outside the US and some suppliers sell 1.5 or 3 cubic foot bags. This calculator assumes the standard 2 cubic foot bag.
- Playground safety surfacing is a different product and a different depth — engineered wood fibre at 9–12 inches, not landscape bark.
Frequently asked questions
How many bags of mulch are in a cubic yard?
Thirteen and a half, using standard 2 cubic foot bags, since a cubic yard is 27 cubic feet. In practice you would buy 14. Bulk is usually cheaper per cubic foot but carries a delivery fee.
How deep should mulch be?
Three inches suits most beds — enough to block light from weed seeds without holding water against stems. Two inches is enough for moisture retention alone, and anything over four inches risks suffocating shallow roots.
How much does a cubic yard of mulch cover?
About 108 square feet at 3 inches deep, 162 square feet at 2 inches, and 81 square feet at 4 inches. Coverage falls as depth rises, because a cubic yard is a fixed 27 cubic feet.
Is bulk mulch cheaper than bags?
Per cubic foot, almost always — often by half. But bulk carries a delivery fee, so the crossover is usually around two cubic yards. Below that, bags frequently work out cheaper once delivery is counted.
How much mulch do I need for a tree ring?
Treat it as a circle with the trunk area removed. An 8 foot ring around a 1 foot trunk is 49.5 square feet, which at 3 inches deep is 12.4 cubic feet, or about 7 bags.
Should mulch touch the tree trunk?
No. Mulch piled against bark traps moisture and causes rot, and the resulting "mulch volcano" is a common way to kill a young tree. Leave a few inches of bare soil around the trunk flare.
Sources and review
Last reviewed .