To work out how much mulch you need, multiply the area (in square feet) by the mulch depth (in inches), then divide by 12 to get cubic feet. Divide that by 27 to get cubic yards. A single cubic yard of mulch covers about 108 square feet at a 3-inch depth, and our free mulch calculator below does the sums for you, including bags, circles, tree rings and more than one bed.
Mulch Calculator
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How the Mulch Calculator Works
This mulch calculator turns the shape of each bed into an area, multiplies that by your chosen depth, adds a small allowance, and then converts the volume into cubic feet, cubic yards and bags. You can add several beds, so one total covers a border, a vegetable patch and a few tree rings in one go. Think of it as a mulch coverage calculator and a bag counter in one tool.
- Pick your units and mulch type. Choosing a material sets a sensible starting depth, which you can change.
- Enter each area. Use a rectangle for most beds, a circle for round beds, and the tree ring option when you need to leave a gap around a trunk.
- Keep the 10% allowance. Mulch settles after it is spread and the edges are rarely perfect, so a small buffer prevents a second trip.
- Choose a bag size or enter a bulk price. The result shows both the number of bags and the volume to order in bulk.
The Mulch Formula, Step by Step
You do not need a mulch calculator for a quick check, and knowing the sum helps you sanity-check any result. The formula is the same for any rectangular bed:
Length (ft) × width (ft) × depth (in) ÷ 12 = cubic feet. Cubic feet ÷ 27 = cubic yards.
For a bed 10 feet long and 12 feet wide with a 3-inch layer:
- Area: 10 × 12 = 120 square feet
- Volume: 120 × 3 ÷ 12 = 30 cubic feet
- Add 10% for settling: 30 × 1.1 = 33 cubic feet
- In cubic yards: 33 ÷ 27 = about 1.22 cubic yards
- In 2-cubic-foot bags: 33 ÷ 2 = 16.5, so buy 17 bags
For other shapes, work out the area first. A circle is π × radius × radius (π is roughly 3.14). A tree ring is the area of the outer circle minus the area of the circle you leave bare around the trunk. A triangle is half the base times the height.
How Much Does a Cubic Yard of Mulch Cover?
If you use a mulch calculator in cubic yards, it helps to know the basics. One cubic yard is 27 cubic feet, so it covers 324 square feet at a depth of 1 inch. The coverage falls in direct proportion as you spread it thicker.
| Mulch depth | Area covered by 1 cubic yard | Area covered by a 2 cu ft bag | Area covered by a 3 cu ft bag |
|---|---|---|---|
| 1 inch | 324 sq ft | 24 sq ft | 36 sq ft |
| 2 inches | 162 sq ft | 12 sq ft | 18 sq ft |
| 3 inches | 108 sq ft | 8 sq ft | 12 sq ft |
| 4 inches | 81 sq ft | 6 sq ft | 9 sq ft |
These figures assume loose mulch measured by volume and no settling, so they are the best case. For bags, remember that a cubic yard equals 9 three-cubic-foot bags, 13.5 two-cubic-foot bags or 18 bags of 1.5 cubic feet.
How Deep Should Mulch Be?
For most beds, 2 to 3 inches of organic mulch is the right range. The Royal Horticultural Society advises spreading mulch at least 5 cm (2 in) deep, ideally 7.5 cm (3 in), and leaving a 10 cm (4 in) mulch-free circle around woody stems. Iowa State University Extension suggests 3 to 4 inches of wood chips on well-drained sites and 2 to 3 inches on heavy soils, keeping mulch at least 6 inches from tree trunks.
The reason is biology rather than tidiness. A layer thinner than about 2 inches lets light through, so weed seeds still germinate. A layer much thicker than 4 inches can keep the soil too wet and make it harder for air and water to reach roots. Mulch piled against a trunk or stem stays damp and can encourage rot, so always pull it back slightly rather than building a volcano shape.
Choosing the Right Mulch Type
| Mulch type | Best for | Worth knowing |
|---|---|---|
| Wood chips or shredded bark | Trees, shrubs, borders, paths | Breaks down slowly and improves soil over time. Top up as it thins. |
| Compost | Vegetable beds and flower borders | Feeds the soil as it breaks down but may let more weeds through, so keep it fresh and weed first. |
| Pine straw or leaf mulch | Acid-loving plants, informal beds | Light and airy, so it settles faster than bark. |
| Rubber mulch | Playgrounds, paths | Does not decompose or add nutrients. Surfacing depth for play areas depends on fall height and the product’s safety rating. |
| Stone or gravel | Dry, sunny beds and drainage areas | Permanent, but heavy to move and it does not improve the soil. |
If you grow plants that dislike wet roots, such as the species in our guide to drought-resistant plants, a thinner organic layer or a stone mulch is often the safer choice.
When to Mulch
Work out how much mulch you need with the mulch calculator first, so you can order before the busy spring rush.
The best time is late winter or early spring, before weed seeds germinate and while the soil is damp but not frozen or waterlogged. The RHS also notes that mulching can be done in autumn through winter. Wait if the ground is very wet or frozen, because mulching over cold, dry or waterlogged soil traps the wrong conditions underneath.
Not sure what to do in the garden this month? Our garden calendar shows the main seasonal jobs.
Common Mulching Mistakes
- Mulching over weeds. Clear perennial weeds first, or they will push through.
- Piling mulch against stems or trunks. Leave a clear gap so bark stays dry.
- Spreading it too thick. More than 4 inches rarely helps and can smother roots.
- Ignoring settling. Without an allowance, the bed looks thin within weeks.
- Using the wrong amount for containers. Pots need a thin top layer. Our guide to container gardening on patios covers how to keep pots from drying out.
Planning Soil and Mulch Together
Mulch works best on top of healthy soil. If you are filling a new bed first, use our soil calculator to work out how much soil you need, then come back here for the mulch on top. For potting mixes and what goes into them, see our guide to the best soil mix for every type of plant. If you are planning a whole bed, our low-maintenance outdoor plants and year-round colour guides are good places to start.
At Patch Plants, every guide is written by botanist Sawera Shahid, and the tools here follow the same approach: practical numbers, checked against sources such as the RHS and university extension services, so you can plan a bed with confidence.
Frequently Asked Questions
How many bags of mulch are in a cubic yard?
A cubic yard holds 27 cubic feet. That equals 9 bags of 3 cubic feet, 13.5 bags of 2 cubic feet, or 18 bags of 1.5 cubic feet. Round up to the next whole bag when you buy.
How many square feet does a cubic yard of mulch cover?
It covers 324 square feet at 1 inch deep, 162 square feet at 2 inches, 108 square feet at 3 inches and 81 square feet at 4 inches. These figures do not allow for settling, so add about 10% to your order.
How much mulch do I need around a tree?
Use the tree ring option in the calculator. Enter the outer diameter of the mulched circle and the diameter of the gap you want to leave at the trunk, then use a depth of 2 to 4 inches. Keep the mulch pulled back from the trunk, at least 4 to 6 inches according to the RHS and Iowa State Extension, so the bark stays dry.
Should I use bulk mulch or bagged mulch?
The mulch calculator shows both. Bags are easier to carry and store, and suit small beds of a few cubic feet. Bulk delivery is usually cheaper per cubic yard for larger areas, so once you need a cubic yard or more it is worth comparing prices. Enter both prices into the calculator to see the difference for your project.
Can I use this calculator for rubber mulch, gravel or playground mulch?
Yes, the volume sum is the same for any loose material, so this mulch calculator can give you the cubic yards and bag count for rubber or stone as well. The depth is a different matter. For playground surfacing, follow the manufacturer’s rated depth for your fall height and the ASTM and CPSC guidance, rather than the default shown here. Bags of rubber and stone also vary in size, so check the label.