Mulch Calculator: How Much Mulch Do I Need?

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.

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.

Cubic yards to bags and coverage

Ordering by the yard? This table turns common bulk amounts into bag counts and the area they cover. Each cubic yard is 27 cu ft; round half bags up when you buy.

Bags of mulch by bed size

How much to buy for common bed sizes at 2 and 3 inches deep, with bags rounded up as the calculator does. Each square foot takes 1/4 cu ft of mulch at 3 inches and about 1/6 cu ft at 2 inches. Bagged mulch is commonly sold in 2 and 3 cu ft bags; for another size, divide the cubic feet by the size on the label and round up.

Mulch for round beds and tree rings

For a round bed, multiply 3.14 by the radius (half the diameter) times itself, then work out the volume as usual. This table does it for common sizes at 3 inches deep, with bags rounded up. At 2 inches, you need two thirds of the cubic feet shown.

Around a tree, UF/IFAS Extension says the mulched area should be at least 8 feet in diameter and should reach the drip line or beyond when you can. Leave the base of the trunk bare and subtract that circle: an 8 ft ring with a 2 ft bare center is 3.14 × (4 × 4 − 1 × 1) = 47.1 sq ft, which at 3 inches is 11.8 cu ft, or 6 bags of 2 cu ft or 4 bags of 3 cu ft. Type 47.1 as the length and 1 as the width and the calculator gives the same result.

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.

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.

Pine straw is sold by the bale rather than by the cubic foot. A Texas A&M extension guide says a 40 lb bale typically covers about 100 sq ft, a 10 × 10 ft bed, to a 2 inch depth, so at that depth divide your square footage by 100 for a rough bale count. For new beds, the same guide calls for about 3 inches of pine straw, which settles to about 1.5 inches, so a new bed takes more than one bale per 100 sq ft.

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.

Using decorative stone instead of wood? The gravel calculator works in cubic yards and tons.

Rubber mulch under play equipment

Under a swing set or play structure, mulch is a safety surface, so its depth follows playground guidance rather than garden rules. The CPSC Public Playground Safety Handbook says never to use less than 9 inches of loose-fill material, except shredded or recycled rubber, for which it recommends 6 inches. At 6 inches, every 100 sq ft takes 50 cu ft, or 1.85 cubic yards. Wood chips and similar loose fill compress at least 25 percent over time, so the handbook's example fills 12 inches to keep 9. Choose rubber mulch made for playgrounds and tested to ASTM F1292, and follow the maker's minimum fill depth.

Fall leaves and winter mulch

Shredded fall leaves make a good mulch, and the volume math is the same: 100 sq ft at 2 inches takes 16.7 cu ft. Shred them first; Penn State Extension notes that shredded leaves mat down less than whole leaves.

Winter mulch goes on late. University of Wisconsin-Madison Extension says it is typically applied when the ground is about to freeze; in Wisconsin, that is close to Thanksgiving weekend or just before the first snow.

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.

How often to re-mulch, and how much to add

Top up when the layer thins rather than starting over. UF/IFAS Extension says that when the depth falls below 2 inches, it is time to replenish with a thin new layer on top, and University of Maryland Extension advises adding only enough to replace what has broken down, up to 3 inches. Here is what 100 sq ft needs to get back to 3 inches:

For a bigger bed, enter only the depth you are adding in the calculator's depth field: 400 sq ft with 2 inches left needs 33.3 cu ft, or 17 bags of 2 cu ft. Pine straw breaks down and settles quickly, so UF/IFAS expects it to need re-mulching often.

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.