Mulch Calculator

The formula

Coverage and yield assumptions

Retail bags are usually 2 cu ft (some premium mulches 1.5 or 3 cu ft). Bulk mulch is sold by the cubic yard, which equals 27 cu ft, or 13.5 two-foot bags. One cubic yard spread 3 in deep covers about 108 sq ft.

How deep should mulch be?

The University of Maryland Extension and most other extension services recommend 2–3 in of organic mulch on beds, and no more than 4 in around trees. Keep mulch a few inches away from tree trunks and plant stems; "volcano" piles against bark invite rot and pests. Topping up an existing bed often needs only 1 in.

Choosing a mulch

Shredded hardwood knits together and stays on slopes. Pine bark nuggets last longer but float in heavy rain. Pine straw is light, acidic and popular in the Southeast. Dyed mulch keeps color for a season. Compost and leaf mold feed the soil but break down quickly. Rubber and stone mulches do not decompose and are better suited to playgrounds and paths than planting beds.

Measuring odd-shaped beds

For a curved bed, lay a garden hose along the edge, then measure the longest length and an average width. For a circle around a tree, area = 3.14 × radius². Triangles are half of base × height. Enter an equivalent length and width that give the same area.

Bulk delivery tips

• Bulk is usually cheaper above about 2–3 cu yd and saves plastic.
• Ask for delivery onto a tarp near the beds to protect the lawn.
• Pull weeds and edge beds before spreading.
• Water lightly after spreading to settle fine mulch.

Common mistakes to avoid

• Piling mulch against tree trunks.
• Spreading more than 3–4 in, which can starve roots of air.
• Mulching over weeds instead of pulling them first.
• Using fresh wood chips mixed into soil, which ties up nitrogen.
• Underestimating curved beds by measuring only the longest length.

Waste factor

5% covers settling and uneven spreading. Use 10% for freshly tilled beds that will settle, slopes, or rough edges. Fresh mulch also compacts by a fifth or so over the first weeks, so you may top up later.

Imperial and metric

Switch the toggle above the inputs to enter ft ↔ m, in ↔ cm. The page converts metric entries to imperial before calculating, using NIST factors (1 ft = 0.3048 m, 1 in = 2.54 cm), and shows key results in both systems.

Worked examples

Front bed 20 × 5 ft, 3 in

Inputs: bed length 20 ft; bed width 5 ft; mulch depth 3 in; waste factor 5%.

Result: You need 0.97 cubic yards of mulch.

• Units to buy (rounded up): 14 2 cu ft bags
• Bed area: 100 sq ft (9.3 m²)
• Volume: 26.3 cu ft (0.74 m³)
• 2 cu ft bags: 14
• 3 cu ft bags: 9

Large border 60 × 6 ft, 3 in

Inputs: bed length 60 ft; bed width 6 ft; mulch depth 3 in; waste factor 10%; cost per unit $4.25.

Result: You need 3.67 cubic yards of mulch.

• Units to buy (rounded up): 50 2 cu ft bags
• Bed area: 360 sq ft (33.4 m²)
• Volume: 99 cu ft (2.8 m³)
• 2 cu ft bags: 50
• 3 cu ft bags: 34
• Estimated material cost: $212.50

Top-up 30 × 4 ft, 1 in

Inputs: bed length 30 ft; bed width 4 ft; mulch depth 1 in; waste factor 5%.

Result: You need 0.39 cubic yards of mulch.

• Units to buy (rounded up): 6 2 cu ft bags
• Bed area: 120 sq ft (11.1 m²)
• Volume: 10.5 cu ft (0.3 m³)
• 2 cu ft bags: 6
• 3 cu ft bags: 4

Quick reference for common sizes

The table repeats the first worked example at smaller and larger sizes, keeping every other setting the same, so you can see how the mulch calculator result scales.

Limitations

Results assume an even depth. Bag sizes and bulk yard measures vary slightly by supplier. Inorganic mulches such as rock are better estimated with the gravel calculator, which accounts for weight.