How to use the mulch calculator
- Choose US (feet and inches) or metric (meters and centimeters).
- Pick the bed shape: a rectangle, a circle (such as a ring around a tree), or a known area if you've already measured the square footage.
- Enter the dimensions and the depth of mulch you want.
- Choose the bag size you plan to buy: 2 cu ft and 3 cu ft are the common sizes in US garden centers, and 50 L is common elsewhere.
- Optionally enter a price per bag and a bulk price to compare the two.
How mulch volume is calculated
Depth is the only measurement in inches, so the calculator converts it to feet before multiplying. Bulk mulch is sold by the cubic yard in the US (a cube 3 ft on each side, or 27 cubic feet) and by the cubic meter elsewhere. Bagged mulch is sold by the cubic foot or the liter: a 2 cu ft bag holds about 57 liters.
Worked example
The defaults are a 20 ft × 10 ft bed covered 3 inches deep, with 2 cu ft bags:
- Area: 20 × 10 = 200 sq ft
- Depth in feet: 3 ÷ 12 = 0.25 ft
- Volume: 200 × 0.25 = 50 cu ft
- In cubic yards: 50 ÷ 27 = 1.85 cubic yards (1.42 m³)
- Bags: 50 ÷ 2 = 25 bags of 2 cu ft, or 50 ÷ 3 = 16.7, so 17 bags of 3 cu ft
At $4 a bag, 25 bags cost $100. At $40 a cubic yard delivered, the same mulch in bulk costs 1.85 × $40 = $74, though most suppliers have a minimum order and a delivery fee. A ring around a tree 8 ft across at the same depth needs π × 8² ÷ 4 × 0.25 = 12.57 cu ft, or 0.47 cubic yards.
How deep to spread mulch
| Use | Depth |
|---|---|
| Annual and perennial flower beds | 2–3 in (5–8 cm) |
| Shrub borders and tree rings | 3–4 in (8–10 cm) |
| Smothering weeds on new beds | 4 in (10 cm), over cardboard or paper |
| Paths and play areas (wood chips) | 4–6 in (10–15 cm), more under swings |
| Topping up last year's mulch | 1 in (2–3 cm) |
Deeper isn't always better. More than about 4 inches on planting beds can keep water and air from reaching the roots. Keep mulch a few inches away from tree trunks and stems; piling it against the bark ("volcano mulching") traps moisture and invites rot and pests.
Bags or bulk?
Bags are easier for small jobs, and they can go in a car trunk. Bulk is usually cheaper per cubic yard once you need more than 2 to 3 cubic yards, which is about 40 bags of 2 cu ft. Ask whether the bulk price includes delivery, and have a tarp ready where the truck can dump the load.
Frequently asked questions
How many bags of mulch are in a cubic yard?
A cubic yard is 27 cubic feet, so it takes 13.5 bags of 2 cu ft (buy 14) or 9 bags of 3 cu ft. In liters, a cubic yard is about 765 L, or 16 bags of 50 L.
How much area does a cubic yard of mulch cover?
At 3 inches deep, one cubic yard covers 108 square feet. At 2 inches it covers 162 sq ft, and at 4 inches 81 sq ft. The formula is 324 ÷ depth in inches.
How do I measure an irregular bed?
Break it into rectangles and circles, or walk the outline with a tape and estimate the average length and width. You can also add up the parts in the square footage calculator and enter the total with the known area option.
Can I use this for wood chips, bark or compost?
Yes. Volume is the same for any loose material sold by the cubic yard or bag. For heavy materials such as gravel, stone or topsoil, which are often sold by weight, use the gravel calculator instead.
Related calculators
- Gravel Calculator — Volume and weight of gravel, crushed stone, sand or topsoil for an area and depth, in tons or tonnes, with cost.
- Square Footage Calculator — Add up the area of up to six rectangles, circles, triangles, trapezoids or L-shapes in sq ft or m², with cost.
- Concrete Calculator — Concrete for slabs, footings, round columns, circular pads and steps, in cubic yards or m³, plus bags needed.
- Volume Calculator — Volume of a cube, box, cylinder, cone, sphere, pyramid, capsule or tube, in cubic units, liters and gallons.
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