Mulch is sold two ways: loose by the cubic yard from a landscape supplier, or bagged in 2 and 3 cubic foot bags at the garden centre. Both come down to one number, the volume of the layer you are about to spread, which is simply the area of the bed times the depth. This calculator does that conversion, tells you how many bags that is, and estimates the weight so you know whether it fits in your car or needs a delivery.
How it is calculated
- Area of the bed: length × width for a rectangle, π × (diameter ÷ 2)² for a circle, or the two rectangles added together for an L-shape.
- Volume = area × depth, with the depth converted from inches to feet (÷ 12) or from centimetres to metres (÷ 100).
- Multiply by the number of beds, then convert: 27 cubic feet per cubic yard, 35.31 cubic feet per cubic metre.
- Bags: divide the cubic feet by 2 or 3 and round up. A cubic yard is 13.5 bags of 2 ft³ or 9 bags of 3 ft³.
- Weight = cubic yards × the loose density of the material, using the EPA volume-to-weight table: 500 lb per cubic yard for shredded wood chips, about 810 for bark, 465 for loose compost, 74 for pine needles.
Example
A 20 × 10 ft bed at 3 inches deep: 200 ft² × 0.25 ft = 50 ft³, which is 1.85 cubic yards (1.42 m³). That is 25 bags of 2 ft³ or 17 bags of 3 ft³. In shredded bark it weighs roughly 1,500 lb, so it is a delivery, not a car trip. At $45 a yard, about $83 of material.
How deep, and why not deeper
Penn State Extension puts the limit at 2 to 4 inches of organic mulch, less on poorly drained soil. Two to three inches is enough for a planted bed; three to four holds weeds down. Beyond four inches the layer stops water and air reaching the roots, and the roots respond by growing up into the mulch where they dry out. Mulch piled against a trunk is worse: the bark stays wet, decays, and gives insects and voles a way in. Spread it wide to the drip line and keep the root flare visible.
Bags or bulk
If you have not measured the bed yet, the square footage calculator handles rectangles, circles and odd shapes you walk out side by side. Bagged mulch makes sense up to about a cubic yard: 14 bags of 2 ft³ is a car load and costs roughly $4–6 a bag. Past that, bulk is half the price per yard and one trip for the supplier instead of ten for you. A cubic yard of bark or chips weighs 500–900 lb, well inside a pickup bed; three yards of wet bark is over a ton and wants a trailer or delivery.
Buying by weight
Some suppliers sell mulch by the ton rather than the yard, which makes comparison awkward because the weight depends entirely on moisture. The same bark that weighs 800 lb a yard dry can weigh half again as much after a week of rain. If you are quoted a price per ton, ask what conversion they use, and treat the weight figure here as a rough dry-material estimate rather than a delivery ticket.
Frequently asked questions
How many bags of mulch are in a cubic yard?
A cubic yard is 27 cubic feet: 13.5 bags of 2 ft³ or 9 bags of 3 ft³. Two cubic yards is 27 of the small bags, which is the point where bulk delivery usually gets cheaper.
How much area does a cubic yard of mulch cover?
At 3 inches deep, 108 square feet. At 2 inches, 162 square feet; at 4 inches, 81 square feet. In metric a cubic metre covers about 13 m² at 7.5 cm.
How deep should mulch be?
Two to three inches in planted beds, three to four to suppress weeds, and never more than four inches total. Penn State Extension recommends 2–4 inches of organic mulch and less on poorly drained soil.
How much does a yard of mulch weigh?
Using the EPA conversion table, about 500 lb for shredded wood chips, 810 lb for bark, 465 lb for loose compost and 74 lb for pine needles. Rubber mulch is the outlier at roughly 1,400 lb. Wet material can weigh 50% more.
Can I put new mulch over old mulch?
Yes, but measure the old layer first and top up to the target depth rather than adding a full new layer. Rake the old mulch to break up any crust, and if the total is already at 3–4 inches, skip a year.
Sources
- Penn State Extension: Mulching landscape trees — 2–4 in depth, keep mulch off the trunk
- Penn State Extension: Mulch, a survey of available options — depth by bed type and material
- US EPA: Standard volume-to-weight conversion factors — loose densities for wood chips, bark, compost and pine needles
By Calcelate Team. Formula from the sources above.
- 2026-09-15 · Formula and texts checked