Mulch Calculator

What is a mulch calculator?

A mulch calculator tells you how much mulch to buy for a garden bed — in cubic feet, in cubic yards (how bulk mulch is sold and delivered), and in the number of bags (how mulch is sold at the store). You enter the length and width of the bed in feet plus the depth you want in inches, and it returns the order quantity in all three units at once.

It removes the awkward unit juggling that trips most people up: depth is measured in inches, area in feet, bulk mulch is priced by the cubic yard, and bagged mulch comes in 2-cubic-foot sacks. The tool converts every one of those for you so you order the right amount in a single trip instead of running back for more or hauling home a surplus.

How is mulch quantity calculated?

The formula is cubic feet = length × width × (depth ÷ 12), then cubic yards = cubic feet ÷ 27. Length and width are in feet, and depth is entered in inches, so dividing depth by 12 converts it to feet before multiplying. The result is the volume of mulch in cubic feet.

To get cubic yards, divide cubic feet by 27, because there are 27 cubic feet in a cubic yard (3 × 3 × 3 ft). To get bags, divide cubic feet by the bag size: this tool uses the standard 2-cubic-foot bag, so bags = cubic feet ÷ 2, rounded up to the next whole bag because you cannot buy a fraction of a bag.

The terms in plain language:

• Length and width — the footprint of the bed, in feet.
• Depth — how thick the mulch layer is, entered in inches and divided by 12 to convert to feet.
• Cubic feet (ft³) — the raw volume, used to count bags.
• Cubic yards (yd³) — cubic feet divided by 27, the unit bulk suppliers use.

What are some worked examples?

A 20 × 10 ft bed at 3 inches deep needs 50 cubic feet, which is 1.85 cubic yards or 25 bags. Here are three reproducible calculations that match the calculator exactly.

Example 1 — a standard flower bed, 20 ft × 10 ft at 3 inches:

• Cubic feet = 20 × 10 × (3 ÷ 12) = 200 × 0.25 = 50 cubic feet
• Cubic yards = 50 ÷ 27 = 1.85 cubic yards
• Bags = 50 ÷ 2 = 25 bags (2-cubic-foot bags)

Example 2 — a small border, 12 ft × 4 ft at 2 inches:

• Cubic feet = 12 × 4 × (2 ÷ 12) = 48 × 0.1667 = 8 cubic feet
• Cubic yards = 8 ÷ 27 = 0.30 cubic yards
• Bags = 8 ÷ 2 = 4 bags

Example 3 — a large bed, 30 ft × 15 ft at 4 inches:

• Cubic feet = 30 × 15 × (4 ÷ 12) = 450 × 0.3333 = 150 cubic feet
• Cubic yards = 150 ÷ 27 = 5.56 cubic yards
• Bags = 150 ÷ 2 = 75 bags

Tip: once a job passes roughly 6 to 8 bags, compare the price of bulk by the cubic yard — Example 3 at 75 bags is almost always cheaper to buy as 5.56 cubic yards delivered.

How much area does a cubic yard of mulch cover?

One cubic yard of mulch covers about 108 square feet at 3 inches deep. Coverage depends only on depth — the thinner the layer, the more ground a yard spreads across. Use this table to sanity-check an order before you buy.

Depth	Area covered by 1 yd³	Bags (2 ft³) per yd³
1 in	324 sq ft	13.5
2 in	162 sq ft	13.5
3 in	108 sq ft	13.5
4 in	81 sq ft	13.5

Note that 1 cubic yard always equals 27 cubic feet (about 13.5 of the 2-cubic-foot bags) regardless of depth — only the area it covers changes. The 13.5 bags is why 14 bags is the practical, rounded-up count to match one delivered yard.

What are common use cases?

Mulch calculations cover most beds, borders and ground-cover landscaping jobs. Typical projects include:

• Flower and shrub beds — a 2 to 3 inch layer to retain moisture and block weeds.
• Around trees — a ring of mulch kept a few inches clear of the trunk.
• Vegetable gardens — straw or bark mulch between rows to hold soil moisture.
• Pathways and play areas — a thicker 3 to 4 inch layer of wood chips.
• Refresh top-ups — a thin 1 inch layer to revive faded mulch each spring.

For a stone or aggregate base instead of organic mulch, see the gravel calculator for cubic-yard and tonnage estimates.

What are the tips, mistakes and limitations to know?

The biggest mistakes are over-mulching against stems and mixing up depth in inches with depth in feet. Keep these points in mind:

• Do not pile mulch against trunks. A “mulch volcano” traps moisture against bark and invites rot; keep a 2 to 3 inch gap.
• Enter depth in inches, not feet. The calculator divides by 12 for you — typing 3 means 3 inches, not 3 feet.
• Measure irregular beds in sections. Break an L-shaped or curved bed into rectangles, calculate each, and add the cubic-feet results before converting.
• Round up, then check bag size. This tool assumes 2-cubic-foot bags; if your store sells 1.5 or 3 cubic foot bags, the bag count will differ even though cubic feet stay the same.
• Buy a little extra. Order about 10% over for settling and uneven coverage so you are not short on the last few square feet.

Limitations: this tool assumes a flat, even layer over a rectangular footprint and the standard 2-cubic-foot bag. It does not account for slope, heavy settling, or non-standard bag sizes. The coverage figures are planning averages — actual spread varies with mulch type, particle size and how firmly it is packed. Treat the result as a close estimate, round up to whole bags or delivery units, and confirm bag size with your supplier before ordering.

For other material estimates, try the paint calculator for wall coverage or the concrete block calculator for hardscape walls, and find more groundwork tools on the construction calculators page.

These figures are general landscaping estimates, not engineering advice.