Mulch Calculator

How much mulch do I need?

Mulch is a loose layer of bark, wood chips, or straw spread over soil. Extension services recommend 2 to 4 inches deep, with about 3 inches a common choice for shrub beds.

To work out how much mulch you need, multiply the bed’s area in square feet by the depth in inches, then divide by 324 to get cubic yards (or by 12 to get cubic feet). This mulch calculator does that for rectangular, round, and triangular beds, converts the volume into bags of 2, 3, or 1.5 cubic feet, and compares the cost of buying bulk by the yard against buying bags.

The default depth is 3 inches, which suits most shrub and perennial beds. You get cubic yards, the number of bags (always rounded up), bulk cost, bagged cost, cubic feet, and the area covered.

The mulch formula

1. Area (sq ft) = length × width for a rectangle, π × (diameter ÷ 2)² for a circle, or base × height ÷ 2 for a triangle.
2. Cubic feet = area × depth in inches ÷ 12.
3. Cubic yards = cubic feet ÷ 27, or in one step, area × depth in inches ÷ 324.
4. Bags = cubic feet ÷ bag size, rounded up to a whole bag.
5. Bulk cost = cubic yards × price per yard. Bagged cost = bags × price per bag.

The number 324 is just 12 × 27: twelve inches to the foot and 27 cubic feet to the yard.

Worked examples

These use the calculator’s own math, so you can enter the same numbers and get the same answer.

1. Front bed: 20 ft × 10 ft, 3 in deep, 2 cu ft bags, $35/yd bulk, $4/bag

• Area: 20 × 10 = 200 sq ft
• Cubic feet: 200 × 3 ÷ 12 = 50 ft³
• Cubic yards: 50 ÷ 27 = 1.85 yd³
• Bags: 50 ÷ 2 = 25 bags
• Bulk: 1.85 × $35 = $65; bagged: 25 × $4 = $100

2. Tree ring: 8 ft diameter circle, 3 in deep, 2 cu ft bags

• Area: π × 4² = 50.3 sq ft
• Cubic feet: 50.3 × 3 ÷ 12 = 12.6 ft³ (0.47 yd³)
• Bags: 12.6 ÷ 2 = 6.3, rounded up to 7 bags, about $28 at $4 a bag

Remember to leave a few inches of bare ground around the trunk; mulch piled against bark traps moisture and invites rot.

3. Long border: 40 ft × 15 ft, 3 in deep, 3 cu ft bags at $5.50, bulk at $35/yd

• Area: 600 sq ft; cubic feet: 600 × 3 ÷ 12 = 150 ft³
• Cubic yards: 150 ÷ 27 = 5.56 yd³
• Bags: 150 ÷ 3 = 50 bags = $275
• Bulk: 5.56 × $35 = $194

The prices above are example inputs, not quotes. Enter what your garden center or landscape yard charges.

Recommended mulch depth by use

Where	Depth	Why
Refreshing an existing bed	1–2 in	Tops up what has broken down
New shrub or perennial bed	2–4 in (3 in typical)	Enough to block light to weed seeds
Vegetable garden	1–2 in	Fine mulch, straw, or compost
Around trees	2–4 in, out to the drip line if possible	Keep it 3–6 in back from the trunk
Paths	3–4 in	Coarse chips hold up to foot traffic
Play areas	9–12 in	For fall protection; use the playground mulch calculator

Mulch coverage chart

Depth	1 cubic yard covers	One 2 cu ft bag covers	One 3 cu ft bag covers
1 in	324 sq ft	24 sq ft	36 sq ft
2 in	162 sq ft	12 sq ft	18 sq ft
3 in	108 sq ft	8 sq ft	12 sq ft
4 in	81 sq ft	6 sq ft	9 sq ft

Coverage halves every time you double the depth, which is why going from 2 to 4 inches doubles your order.

Bags of mulch per cubic yard

Bag size	Bags per cubic yard	Bags for 2 yd³	Bags for 3 yd³
1.5 cu ft	18	36	54
2 cu ft	13.5 → 14	27	40.5 → 41
3 cu ft	9	18	27

The 2 cu ft bag is the most common size at home centers. Check the label: the volume is printed on the front, and some bags use liters (a 2 cu ft bag is about 57 liters).

Bulk vs bagged: finding the break-even

Bulk mulch is cheaper per yard, but most suppliers add a delivery fee. Bags cost more per yard but need no truck. To see which wins for your job:

• Bagged cost per yard = price per bag × bags per yard. At the calculator defaults ($4 per 2 cu ft bag), that is $4 × 13.5 = $54 per yard.
• Gap per yard = bagged cost per yard − bulk price per yard. At $35/yd bulk, the gap is $54 − $35 = $19.
• Break-even = delivery fee ÷ gap per yard.

Delivery fee (example)	Break-even at a $19/yd gap
$0 (you haul it)	Bulk is cheaper from the first yard
$50	~2.6 yd³ (about 36 bags)
$75	~3.9 yd³ (about 53 bags)
$100	~5.3 yd³ (about 71 bags)

Below the break-even, bags are cheaper; above it, bulk is. Use your own prices; the mulch cost calculator handles delivery fees and labor in one place.

How to measure irregular beds

• Break the bed into shapes. Split curved or L-shaped beds into rectangles, circles, and triangles, run each through the mulch calculator, and add the bags together.
• Average the width. For a kidney-shaped bed, measure the length, take three widths (both ends and the middle), average them, and treat it as a rectangle.
• Circles use diameter. Measure straight across the bed through the center. For a ring around a tree, calculate the full circle, since the trunk takes up very little area.
• Use paces for big areas. One adult step is roughly 2.5 ft; measure yours once against a tape for a quick estimate, then confirm with the square footage calculator.
• Subtract what is already there. If 1 inch of old mulch remains and you want 3 inches, enter a 2-inch depth.

Common mulch mistakes

• Using feet for depth. Depth goes in inches here. Three feet of mulch instead of three inches would be a 12× overorder.
• Mulch volcanoes. Piling mulch high against tree trunks keeps bark wet and can lead to rot and pests. Spread it flat and pull it back from the trunk.
• Too deep a layer. More than 4 inches of mulch can keep soil soggy and cut off air to roots.
• Skipping the edge. Mulch thins out at bed edges. A cut edge or border keeps it in place and keeps the depth even.
• Ignoring bag size. A 3 cu ft bag holds 50% more than a 2 cu ft bag. Compare price per cubic foot, not price per bag.

Choosing a mulch type

Shredded hardwood and bark are the standard for shrub beds. Wood chips are cheaper and coarser, good for paths and tree rings. Pine straw is sold by the bale rather than by volume, and rubber mulch does not break down, so you only buy it once. For bed prep, lay landscape fabric on weedy ground, or add compost underneath; for stone instead of mulch, use the gravel calculator.