Mulch volume for rectangle, circle, and triangle beds from a depth in inches — cubic yards, 2 and 3 cu ft bag counts, and estimated bag cost at your price.
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FORMULA USEDMulch Calculator
Depth drives the whole estimate
Mulch is priced by volume, and volume is just area times depth. Because depth is measured in inches while area is in feet, the formula divides inches by 12: a 100 ft² bed at 3 in needs 100 × 3 ÷ 12 = 25 ft³ of mulch.
The formulas by shape
Rectangle: length × width. Circle: π × radius² — measure from the center of the tree to the edge of the ring. Triangle: base × height ÷ 2. Multiply the area by depth ÷ 12 for cubic feet, then divide by 27 for the cubic yards that bulk sellers quote.
Bags or bulk?
The standard bag is 2 ft³ (a cubic yard is 13.5 of them); some brands sell 3 ft³ bags. A yard of mulch covers 324 ft² at 1 in, 162 ft² at 2 in, or 108 ft² at 3 in — handy for sanity-checking a bulk delivery against your bed area.
Worked example
A foundation bed runs 10 ft × 5 ft, to be topped up 3 in deep.
Area: 10 × 5 = 50 ft².
Volume: 50 × (3 ÷ 12) = 12.5 ft³ = 0.46 yd³.
That is 7 two-cubic-foot bags — about $35 at $5 a bag.
How to use it
Match the shape: rectangle, circle around a tree, or triangle corner.
Enter the bed dimensions and your target depth in inches.
Read the yardage for a bulk order or the bag count for the garden center.
Compare the bag-cost row against a per-yard bulk quote before hauling.
Frequently asked questions
How many bags of mulch are in a cubic yard?
A yard is 27 ft³, so it takes 13.5 of the standard 2 cu ft bags or 9 of the larger 3 cu ft bags. The results board shows both bag counts from your bed dimensions.
How deep should mulch be?
Aim for a finished depth of 2–3 in on established beds and 3–4 in when starting from bare soil. Beyond about 4 in, mulch sheds water and starves roots of air.
How much does a cubic yard of mulch cover?
At 3 in deep, one yard covers about 108 ft². The same yard spreads over 324 ft² at 1 in or 162 ft² at 2 in.
How do I calculate mulch for a circular bed?
Square the radius and multiply by π: a 6 ft radius gives π × 36 ≈ 113 ft². At 3 in deep that is 28.3 ft³, roughly 1.05 yd³ or 15 bags.
Should I remove old mulch every year?
Usually no. Pull back the old layer, check that total depth stays under about 3–4 in, and top dress with an inch of fresh material. Full removal is only needed if the old mulch is matted, moldy, or harboring pests.
Is bagged or bulk mulch cheaper?
Bulk almost always wins on volume — 14 bags equals one yard, and per-bag prices usually total two to three times a landscape yard’s per-yard price. Bags win for small touch-ups and vehicles without a truck bed.