Mulch Calculator

How this calculator works

Mulch is bought by volume, so the whole estimate is area × depth, repeated for every bed and added up. Each bed you add is calculated on its own:

bed area   = length × width          (rectangle)
           = π × (diameter ÷ 2)²     (circle)
new depth  = target depth − existing mulch depth   (never below 0)
bed volume = area × (new depth ÷ 12)   → cubic feet

The totals then convert into the two ways mulch is sold:

bags       = total cu ft ÷ bag size (1.5, 2, or 3 cu ft)  → rounded up
bulk yards = total cu ft ÷ 27       → rounded up to the nearest 0.5 cu yd

The existing-mulch field is what keeps refresh jobs honest: topping up a bed that already has an inch of old mulch takes a third less material than mulching bare soil. If a bed's existing depth already meets the target, it simply contributes zero.

When you enter both a per-bag price and a bulk per-yard price, the calculator totals each option — delivery fee included on the bulk side — tells you which is cheaper and by how much, and uses the cheaper option in the cost summary.

Worked example: two beds

Suppose you're mulching a 10 × 4 ft border bed and a round bed 6 ft across, both at 3 inches:

• Border bed: 10 × 4 = 40 sq ft; 40 × (3 ÷ 12) = 10 cu ft.
• Round bed: π × (6 ÷ 2)² = 28.3 sq ft; 28.3 × (3 ÷ 12) = 7.1 cu ft.
• Total: 17.1 cu ft ÷ 27 = 0.63 cu yd.
• Bags: 17.1 ÷ 2 cu ft per bag = 8.5 → 9 bags.
• Bulk: 0.63 cu yd rounds up to the 1/2-yard increment above it — 1 cubic yard, since suppliers rarely sell less than half a yard at a time.

At this size the choice is genuinely close: nine bags fit in most car trunks, while a bulk yard usually carries a delivery fee that erases its lower per-volume price. Enter your local prices and the calculator will settle it with arithmetic instead of guessing.

How to measure your beds

• Rectangles: measure the longest length and the average width. Beds are rarely perfect rectangles — for a gently curving border, use the width at several points and average them.
• Round beds and tree rings:measure straight across the widest point (the diameter). For a ring around a tree, measure the full circle; the trunk's area is small enough to ignore, and you should keep mulch pulled back from it anyway.
• Odd shapes: split them. An L-shaped bed is two rectangles; a kidney shape is roughly a rectangle plus a circle-half. Add each piece as its own row and let the calculator sum them.
• Existing mulch: push a ruler through the old mulch to the soil in a few spots and average. If it reads 1 inch and you want 3, you only need 2 inches of new material — enter 1 in the existing-depth field.

For more on breaking odd areas into measurable pieces, see How to Calculate Square Footage.

Bags vs. bulk: how to buy mulch

• Rule of thumb: below about a yard and a half, bags usually win once delivery is added; above two to three yards, bulk pricing pulls ahead fast. In between, run both numbers — this calculator does it for you.
• Bags are easier to handle. They stack, stay dry, move one at a time, and leftovers store for next season. A 2 cu ft bag weighs roughly 20–40 lb depending on moisture.
• Bulk is cheaper per yard and less packaging, but it arrives as one pile on your driveway that has to be wheelbarrowed the same week — a yard of hardwood mulch weighs in the neighborhood of 400–800 lb.
• Check what a "scoop" means. Landscape yards often sell by the loader scoop, which may be half a yard or three-quarters — ask, and convert before comparing prices.
• Color and type: dyed mulches hold color longer; natural hardwood and pine bark break down into the soil faster. Whatever you choose, buy the whole job from one batch so the color matches.

Common estimating mistakes

• Guessing depth instead of picking one. The difference between 2 and 4 inches is double the material and double the bill. Decide the depth first — 2–3 inches for most beds — and measure existing mulch before topping up.
• Confusing cubic feet and cubic yards. A cubic yard is 27 cubic feet — thirteen and a half 2 cu ft bags, not nine. Comparing a per-bag price to a per-yard price without converting is the classic way to overpay.
• Ignoring the delivery fee when comparing. A $30 bulk yard with a $50 delivery fee costs $80 for the first yard. On small jobs, that fee decides the bag/bulk question all by itself.
• Measuring beds larger than they are. Mulch only covers the open soil — subtract paths, large boulders, and dense groundcover areas rather than mulching over the plan on paper.
• Piling mulch against trunks.Not an estimating error, but the most common installation one: "mulch volcanoes" hold moisture against bark and invite rot. Keep a 2–3 inch gap around every trunk and stem.

Limitations

The calculator treats every bed as a flat rectangle or circle with a uniform depth. Real beds slope, curve, and thin out at the edges, so treat the result as a close planning number rather than an exact one — most people land within a bag or two. It does not model mulch settling (fresh mulch compresses roughly a third as it settles over the first season), coverage differences between materials like straw or pine needles, or landscape fabric and edging. Bag sizes are limited to the common 1.5, 2, and 3 cu ft options; for odd sizes, pick the closest and adjust by the ratio.