Mulch Calculator

This mulch calculator tells you how much mulch to buy for flower beds, borders, vegetable paths and tree rings. Enter the size of the area and the depth you want, and it shows the volume in cubic yards and cubic feet, the number of 2 and 3 cubic foot bags, and how far one cubic yard will stretch at that depth. A tree ring option subtracts the clear circle you should leave around a trunk, so you do not buy mulch for space that should stay bare.

How to use the mulch calculator

1. Pick the type of area. Choose a rectangle for beds and borders, a round bed for circular plantings, or a tree ring for mulch around a single trunk.
2. Enter the size in feet. For a tree ring, enter the full outer diameter of the mulched circle and the small clear circle you will leave around the trunk.
3. Enter the depth in inches. Most beds need 2 to 3 inches. The section on depth below explains when to go thinner or thicker.
4. Set the number of identical areas. If you are mulching five trees with rings of the same size, enter one ring and set this to 5.
5. Read the result. Use cubic yards when ordering bulk mulch, and the bag counts when buying at a store.

For beds with several shapes, run each part separately and add the totals. An L-shaped border is two rectangles, and a bed with a curved front can be treated as a rectangle using its average width.

The mulch formula

Mulch is calculated the same way as soil: area times depth gives volume. Depth is entered in inches, so it is divided by 12 to convert to feet.

Cubic feet = area (sq ft) × depth (in) ÷ 12
Cubic yards = cubic feet ÷ 27

For a tree ring, the area is the outer circle minus the clear circle at the trunk: 3.1416 × (outer radius² − inner radius²).

Worked example: a long border

A border along a fence is 20 feet long and 4 feet wide, and you want 3 inches of shredded hardwood. The area is 80 square feet. The volume is 80 × 3 ÷ 12 = 20 cubic feet, which is about 0.74 cubic yards. That is 10 bags of 2 cubic feet, or 7 bags of 3 cubic feet.

Worked example: a tree ring

A young maple gets a mulch ring 6 feet across, with a 1-foot clear circle around the trunk. The outer radius is 3 feet and the inner radius is half a foot, so the area is 3.1416 × (9 − 0.25) ≈ 27.5 square feet. At 3 inches deep that is about 6.9 cubic feet, or 4 bags of 2 cubic feet.

Worked example: all the beds around a house

If the beds around a home add up to 400 square feet, 3 inches of mulch is 400 × 3 ÷ 12 = 100 cubic feet, or about 3.7 cubic yards. In bags, that is 50 bags of 2 cubic feet, which is several carloads. At this size, bulk delivery is usually cheaper and much less work.

How deep should mulch be?

Depth is the most important number in any mulch order. Too thin and weeds push through and the soil dries out. Too thick and water struggles to reach the soil, roots can be starved of air, and the layer can stay soggy against stems. University extension guidance for home landscapes generally lands on 2 to 3 inches for most beds.

Coverage per cubic yard

If you know how much area you have and want a quick figure without the calculator, these are the coverage numbers for one cubic yard of mulch:

Halving the depth doubles the area a yard covers. That is why depth matters so much for the budget: going from 2 to 3 inches across a large bed adds 50 percent to the order.

Bagged or bulk mulch?

Bagged mulch is usually sold in 2 cubic foot bags, with some brands and bark products in 3 cubic foot bags. The two sizes look alike on a pallet, so read the label before you count. Bulk mulch is sold by the cubic yard from landscape suppliers, sawmills and some municipal yard-waste sites.

To compare prices, convert both to price per cubic foot. Divide the bag price by its size, and divide the bulk price per yard by 27, then add any delivery fee spread over the order. For small jobs up to roughly half a yard, bags are often simpler. Beyond a yard or two, bulk is usually much cheaper per cubic foot, and it saves dealing with dozens of plastic bags. The mulch bag calculator focuses on that comparison.

Arborists and tree services often have fresh wood chips they will drop for free or a small fee, because it saves them disposal costs. Fresh chips are coarse and variable, but they are excellent for paths and around trees and shrubs.

Choosing a mulch

The best mulch depends on where it goes and what you want it to do. All organic mulches hold moisture, moderate soil temperature and suppress weeds, and they improve the soil as they break down.

• Shredded hardwood knits together into a mat that stays put on slopes and resists washing away. It is a good all-round choice for beds and borders.
• Bark nuggets are coarse and long-lasting, but they can float and wash out in heavy rain. They suit level areas around shrubs.
• Pine straw is light, stays in place well on slopes and is popular in the Southeast. It is usually sold by the bale, so check the coverage printed on the bale.
• Wood chips are economical and durable. They work best on paths and around trees rather than in vegetable beds.
• Straw is the classic vegetable garden mulch. Choose straw rather than hay, which tends to carry weed seed.
• Shredded leaves are free, break down quickly and feed the soil. Shred them first so they do not mat into a waterproof layer.
• Compost can be used as a thin mulch, about an inch, though it breaks down fast and weed seeds can sprout in it. The compost calculator works out how much you need.

Dyed mulches are colored wood products. The color fades over a season or two. Rubber mulch does not break down or improve the soil, so most gardeners reserve it for play areas rather than planting beds.

When and how to apply mulch

Spring and fall are the usual times to mulch. In spring, wait until the soil has warmed a little, because a thick layer applied early can keep cold soil cold for longer. In fall, mulch after the ground has cooled to help insulate roots and limit frost heaving of new perennials.

1. Weed first. Mulch suppresses new weeds from seed, but established perennial weeds will grow straight through it.
2. Water the soil. Mulch slows evaporation, so it is best spread over moist ground.
3. Spread evenly. Dump small piles across the bed and rake them out to an even depth rather than tipping one big pile.
4. Pull mulch back from stems and trunks. Leave a few inches of bare soil around the base of each plant.
5. Edge the bed. A clean edge or a shallow trench at the lawn line stops mulch from spilling into the grass.

Around buildings, many pest-control and extension sources suggest keeping mulch a few inches below siding and leaving a narrow mulch-free strip next to the foundation. This makes it easier to spot termite activity and keeps moisture away from the house.

How often to replace mulch

Organic mulch breaks down over time, which is part of its value. Fine mulches such as shredded leaves may be mostly gone in a season, while bark nuggets can last several years. Rather than adding a fresh 3-inch layer every spring, check the depth. If an inch remains, add one or two inches to bring it back to the target. Piling new mulch onto old year after year is how beds end up buried under 6 or 8 inches, which harms plants.

If old mulch has formed a dense, crusty mat, break it up with a rake before topping up, so water can soak through.

Does wood mulch rob soil of nitrogen?

Wood products need nitrogen to decompose, and this worry comes up often. When wood chips or sawdust are mixed into the soil, they can tie up nitrogen in the root zone for a time. When the same materials sit on the surface as mulch, the effect is largely confined to the thin contact zone between mulch and soil, and established plants are generally not affected. The practical rule is simple: use wood mulches on top, and do not dig them into vegetable beds.

Common mulching mistakes

• Buying by eye. A pallet of bags looks like a lot, but 20 bags of 2 cubic feet only covers 160 square feet at 3 inches deep.
• Spreading too thick. More than about 4 inches on planting beds can keep roots too wet and short of oxygen.
• Piling against trunks and stems. This leads to rot and gives pests shelter.
• Using landscape fabric under fine mulch. Mulch breaks down on top of the fabric, and weeds root into that layer anyway.
• Mixing wood mulch into soil. Keep it on the surface.

Mulching vegetable gardens

Vegetable beds benefit from mulch as much as flower beds, but the best materials are different. Light, fast-breaking mulches such as straw, shredded leaves and grass clippings suit vegetables, because they can be turned into the soil or composted at the end of the season. Wood chips and bark are better kept to paths, where their slow breakdown is an advantage.

Timing matters more in a vegetable garden. Warm-season crops such as tomatoes, peppers and squash like warm soil, so wait until the soil has warmed in late spring before mulching around them. Cool-season crops such as lettuce, peas and broccoli benefit from mulch earlier, because it keeps the soil cool as summer approaches and delays bolting. Grass clippings should go on in thin layers of an inch or so, letting each layer dry before adding more, or they mat and turn slimy. Avoid clippings from lawns treated with herbicides.

For direct-sown crops such as carrots and beans, wait until seedlings are a few inches tall before mulching between rows, so the mulch does not bury them.

Frequently asked questions