Mulch Calculator

Tip: keep mulch a few inches away from tree trunks and plant stems. Mulch piled against bark holds moisture and invites rot and pests.

Worked example

A 20 ft by 4 ft bed along the front of the house is 80 square feet. At 3 inches deep, 80 x 3 / 12 = 20 cubic feet of mulch.

That is 20 / 27 = 0.74 cu yd in bulk. In bags, it takes 10 bags of 2 cubic feet or 7 bags of 3 cubic feet. For a single bed this size, bags are usually the simpler choice.

How to calculate mulch

Measure the length and width of the bed in feet and multiply them to get square feet. Multiply that by the depth in inches divided by 12 to get cubic feet. Bagged mulch is sold by the cubic foot, usually in 2 or 3 cubic foot bags. Bulk mulch is sold by the cubic yard, which is 27 cubic feet.

For curved or odd-shaped beds, split them into rectangles and circles, calculate each one and add the results. A round bed around a tree has an area of 3.14 x radius squared. A bed 6 ft across has a radius of 3 ft and covers about 28 square feet.

How deep should mulch be?

• Refreshing an existing bed: 1 to 2 inches on top of what is there.
• New beds and around shrubs: 2 to 3 inches.
• Paths, play areas and weed-heavy spots: 3 to 4 inches.

Much deeper than 4 inches can starve roots of air and keep the soil too wet. If an existing bed already has a thick layer, rake it loose and add only enough to restore the color.

Quick coverage chart

One cubic yard of mulch covers about:

• 324 square feet at 1 inch deep.
• 162 square feet at 2 inches deep.
• 108 square feet at 3 inches deep.
• 81 square feet at 4 inches deep.

A 2 cubic foot bag covers 8 square feet at 3 inches, and a 3 cubic foot bag covers 12.

Bags or bulk?

Bags are easy to carry, store neatly and suit small jobs. Bulk mulch costs far less per cubic yard and is the better buy once you need more than two or three yards, about 30 to 40 bags. Bulk usually comes with a delivery fee, and you will need a wheelbarrow, a pitchfork and a tarp to protect the driveway.

Bulk mulch is also sold in partial yards at many landscape yards if you have a pickup truck. A full-size pickup bed holds about 2 to 3 cubic yards of mulch, since it is light.

Types of mulch

Shredded hardwood knits together and stays put on slopes. Pine bark nuggets last longer but can float away in heavy rain. Dyed mulch keeps its color for a season. Pine straw is light and good for acid-loving plants. Rubber mulch and stone do not break down, so they do not feed the soil. For stone, use the gravel calculator, since it is sold by weight.

When to mulch

Spring is the most common time to mulch, once the soil has warmed and perennials have started to come up. Mulching too early keeps cold soil cold and slows growth. A fall layer helps insulate roots of shrubs and perennials through winter and keeps the beds tidy until spring.

Before you spread new mulch, pull weeds, edge the beds and water the soil if it is dry. Rake old mulch to break up any crust so water can get through. Landscape fabric under mulch is optional. It helps in beds with no plantings, but it can trap roots and make it harder to add plants later.

More calculators

Results are estimates, not a contractor quote. Check quantities with your supplier before you order, and follow local building codes.