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How much mulch do you need?
Measure your bed or tree ring, pick a depth and a mulch type — the calculator works out cubic feet, cubic yards, bag count and whether bags or bulk delivery is cheaper. No sign-up, no submit button.
Your area
How this is calculated
Like a lab worksheet — here is every step, so you can check the working:
- Area: rectangle
length × width; tree ringπ × (R² − r²), where R is the outer radius and r the trunk radius (diameters ÷ 2). - Cubic feet:
area × (depth ÷ 12)— e.g. a 10 × 4 ft bed at 3 in: 40 × 0.25 = 10 cu ft. - Cubic yards:
cubic feet ÷ 27— there are 27 cubic feet in a cubic yard. - Bags:
cubic feet ÷ bag size, rounded up — you cannot buy part of a bag. - Costs:
bags × price per bagversuscubic yards × bulk price. The cheaper total wins.
What to buy: bags vs bulk
Bags (usually 2 cu ft) win for small jobs — under about 1 cubic yard. They are easy to carry and you buy exactly what the calculator says, rounded up. Bulk (sold by the cubic yard, delivered) usually wins at 1 cubic yard and above. A yard of mulch delivered often costs less than the equivalent bags, but you will need somewhere to tip the pile and a wheelbarrow to move it.
The calculator compares material cost only. Bulk delivery fees vary — add them before you decide. Bulk suppliers usually sell by the full or half yard, so round up when you order.
Sources & assumptions
Volume maths is standard geometry. Bag sizes (2 and 3 cu ft) are the common retail sizes; bulk mulch is sold by the cubic yard. Depth guidance (2–4 in for most mulches, kept back from stems and trunks) follows US cooperative extension mulch publications. Mulch type does not change the volume maths — only the depth you should aim for and the price you pay. Prices vary by region; the cost comparison is only as good as the prices you enter.
Want the full explanation?
How deep mulch should be for beds, paths and trees, a ready-reckoner table for common bed sizes, and when bulk beats bags.
Mulch calculator FAQ
How deep should mulch be?
For most mulches, 2–4 inches. Keep it 2–3 inches back from stems and trunks — mulch piled against bark holds moisture and invites rot. Straw is the exception: lay it 4–6 inches deep and loose, since it settles to about half.
Bags or bulk — which is cheaper?
It depends on the job size and local prices. Enter your bag price and bulk price per cubic yard above and the calculator compares the two. As a rough guide, bulk usually wins above about 1 cubic yard, but delivery fees can change the answer — add them in before you decide.
Does mulch type change how much I need?
No. The volume maths is identical whatever you spread — type only changes the recommended depth and the price. That is why the calculator asks for type (for the tip) but the volume never changes with it.
How do I measure a tree ring?
Measure the outer diameter of the mulched ring and the trunk diameter at the middle. The calculator subtracts the trunk circle (a tree does not need mulch under its own trunk) using π(R²−r²).
Should I put landscape fabric under mulch?
Extension guidance generally says no for planting beds. Mulch alone suppresses weeds while letting water and air through; fabric eventually clogs, lifts, and makes replanting miserable.