Mulch Calculator: How Much Mulch Do I Need?

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To figure out how much mulch you need, do what our mulch calculator does: multiply the bed's length by its width in feet, multiply by the depth in inches, and divide by 12 to get cubic feet; divide that by 27 for cubic yards, or by the bag size for a bag count. As a rule of thumb, one cubic yard covers about 108 square feet at 3 inches deep, and a 2 cu ft bag covers about 8 square feet at that depth. Most shrub and flower beds need 2 to 3 inches of shredded wood or bark.

Enter your bed size below and the calculator converts it to cubic yards and bags.

How much mulch do you need?

Enter the bed size and depth. Results in cubic yards and bags.

ft
ft
in

A 2 to 3 inch layer is typical for garden beds. Bagged mulch usually comes in 2 or 3 cu ft bags; bulk mulch is sold by the cubic yard (27 cu ft).

How to measure your beds

  1. Sketch each bed and break it into simple shapes: rectangles, circles, and triangles. Measure each shape's length and width in feet. For long borders, a 100 ft tape or a measuring wheel is faster and more accurate than a short tape.
  2. For a round bed or a ring around a tree, measure the diameter, divide by 2 to get the radius, then multiply 3.14 × radius × radius. For a triangle, multiply the two sides that meet at the square corner and divide by 2.
  3. Add up the square footage of every shape. Subtract large areas that won't get mulch, such as a patio slab or a big boulder. You can ignore individual plants; they barely change the total.
  4. Pick your depth and check what is already on the ground. Push a trowel or ruler down through the old mulch until you hit soil. If 1 inch is left and you want 3 inches, you only need to add 2.
  5. Enter the numbers. For odd shapes you have already added up, a quick trick is to type the total square footage as the length and 1 as the width.
Mulch: bed size and depthPlan of a 20 by 4 foot garden bed and a cross-section showing a 3 inch layer of mulch over the soil. 20 ft times 4 ft times 3 in, divided by 12, is 20 cubic feet; divided by 27 that is 0.74 cubic yards, or 10 bags of 2 cu ft or 7 bags of 3 cu ft.BED SIZE AND DEPTH20 ft4 ftCross-sectionmulchsoil3 in4 ft20 cu ft20 ft × 4 ft × 3 in ÷ 120.74 cu yd20 cu ft ÷ 27 cu ft per cu yd0.74 cu yd (20 cu ft)10 bags of 2 cu ft or 7 bags of 3 cu ft
Measure the bed's length and width and pick a depth: 20 ft x 4 ft at 3 in deep is 20 cu ft, or 0.74 cubic yards.

The mulch formula

The calculator runs the same volume math you would do on paper:

  • Cubic feet = length (ft) × width (ft) × depth (in) ÷ 12
  • Cubic yards = cubic feet ÷ 27
  • Bags = cubic feet ÷ bag size, rounded up to a whole bag

Dividing by 12 turns the depth from inches into feet. The 27 comes from the size of a cubic yard: 3 ft × 3 ft × 3 ft = 27 cubic feet. Iowa State University Extension teaches the same method: find the bed area, multiply by the mulch depth in feet, then divide by the bag size or by 27 for bulk.

Worked example (the calculator's default values)

Say you have a border bed 20 ft long and 4 ft wide, and you want mulch 3 inches deep.

  1. Area: 20 × 4 = 80 sq ft
  2. Volume: 80 × 3 ÷ 12 = 20.0 cu ft
  3. Cubic yards: 20 ÷ 27 = 0.74 cubic yards
  4. 2 cu ft bags: 20 ÷ 2 = 10 bags
  5. 3 cu ft bags: 20 ÷ 3 = 6.67, rounded up to 7 bags

The calculator shows the same result: "You need 0.74 cubic yards of mulch (20.0 cu ft). That is 10 bags of 2 cu ft or 7 bags of 3 cu ft." For one bed this size, bags are the easy choice. Once a whole-yard project adds up to several cubic yards, bulk becomes worth pricing, because bulk mulch generally costs less per cubic foot than bagged.

One cubic yard is 27 cubic feetA 3 by 3 by 3 foot cube divided into 27 one-foot cubes, which is one cubic yard. A 20 cubic foot mulch order fills 20 of the 27 cubes, or 0.74 cubic yards. The same 20 cubic feet is 10 bags of 2 cu ft or 7 bags of 3 cu ft.CUBIC FEET TO CUBIC YARDS3 ft3 ft3 ft1 cu yd = 27 cu ft3 ft × 3 ft × 3 ftYour bed: 20 cu ft20 ÷ 27 = 0.74 cu yd(20 of the 27 cubes)Or in bags:10 bags × 2 cu ft7 bags × 3 cu ft
One cubic yard is 27 cu ft, so a 20 cu ft order is 0.74 cubic yards, or 10 bags of 2 cu ft or 7 bags of 3 cu ft.

Mulch coverage chart

Use this chart to sanity-check an order or to size a bulk delivery. The numbers are straight volume math for a level bed.

Depth1 cubic yard coversOne 2 cu ft bag coversOne 3 cu ft bag covers
1 in324 sq ft24 sq ft36 sq ft
2 in162 sq ft12 sq ft18 sq ft
3 in108 sq ft8 sq ft12 sq ft
4 in81 sq ft6 sq ft9 sq ft

One cubic yard is the same volume as 13.5 bags of 2 cu ft or 9 bags of 3 cu ft. That is a handy number when you compare a bulk quote with a stack of bags.

How deep should mulch be?

Depth depends on the material. Iowa State University Extension gives 2 to 4 inches as the general range, with coarse mulches like wood chips toward the deeper end and finer ones like grass clippings toward the shallower end. Loose materials such as straw and hay go on much thicker.

Mulch typeSuggested depth
Shredded hardwood2 to 3 in
Pine bark2 to 3 in
Compost2 to 3 in
Pine needles3 to 4 in
Shredded leaves3 to 4 in
Straw or grass hay6 to 8 in

Depths above are from the University of New Hampshire Cooperative Extension garden mulch fact sheet. If you are not sure, 3 inches of shredded bark is a sensible default for most ornamental beds, and it is what the calculator starts with.

Around trees, the University of Vermont Extension describes a simple "3-3-3" guide: keep mulch at least 3 inches from the trunk, no more than 3 inches deep, and in a ring about 3 feet across. Penn State Extension recommends extending the ring toward the drip line, the outer edge of the canopy, when you have room.

Tips for buying and spreading mulch

  • Read the bag size. Bagged mulch is commonly sold in 2 cu ft bags (Scotts Nature Scapes, for example) and 3 cu ft bags (common for pine bark nuggets). If your bag is a different size, divide the cubic feet from the calculator by that size and round up.
  • Measure every bed, then add them. Front beds, tree rings, and the narrow strip along the driveway add up fast. Run the calculator once per area or add the square footage first.
  • Top up instead of starting over. Old mulch breaks down, but some usually remains. If an inch is left and your target is 3 inches, you need a third less than a bare bed would.
  • Time it well. Iowa State Extension suggests early spring, after the soil warms and perennials come up, or fall after plants go dormant. Mulching too early in spring can slow emergence.
  • Spread from the middle out. Dump small piles across the bed, then rake them level. It is easier to hit an even depth than to push one big pile around.
  • Round up. A spare bag in the garage costs less effort than a second trip for one more.

Common mistakes to avoid

  • Volcano mulching. Piling mulch in a cone against a tree trunk traps moisture against the bark, which encourages decay and gives insects, disease, and rodents a way in. Pull mulch back so the root flare stays visible.
  • Going too deep. Iowa State Extension advises keeping mulch no more than 4 inches deep, and Gardener's Supply warns that deeper layers risk smothering roots.
  • Ignoring the mulch that is already there. Adding a full 3 inches on top of 2 inches of old mulch puts you at 5 inches.
  • Mixing inches and feet. The depth field is in inches. Typing 0.25 (a quarter foot) instead of 3 gives you a result that is twelve times too small.
  • Mulching right against stems. UNH Extension recommends keeping mulch 2 to 3 inches away from the base of plants to discourage disease and rodents.

Frequently asked questions

How many bags of mulch are in a yard?

A cubic yard is 27 cubic feet. That equals 13.5 bags of 2 cu ft or 9 bags of 3 cu ft. Round up when you buy, since stores don't sell half bags.

How much area does a yard of mulch cover?

At 3 inches deep, one cubic yard covers about 108 square feet. At 2 inches it covers about 162 square feet, and at 4 inches about 81 square feet.

Should I remove old mulch before adding new?

Not usually. Check how much is left, then add only enough to reach your target depth. If it has built up too thick, rake some out so the total stays at or under about 4 inches, and always pull it away from trunks and stems.

How much mulch do I need around a tree?

For a ring 6 ft across at 3 inches deep: the radius is 3 ft, so the area is 3.14 × 3 × 3 = 28.3 sq ft. Multiply by 3 and divide by 12 to get 7.1 cu ft, which is 4 bags of 2 cu ft. Leave a gap of at least 3 inches around the trunk.

Is bagged or bulk mulch better?

Bagged mulch is easier to carry, store, and spread in small amounts. Bulk mulch is sold by the cubic yard and generally costs less per cubic foot, so it tends to win on larger jobs. Some suppliers have delivery minimums, so ask before you order.

When is the best time to mulch?

Spring after the soil has warmed and perennials have emerged, or fall once plants are dormant. You can top up during the season whenever bare soil shows through.