Mulch Calculator

1. Pick Imperial or Metric and the bed shape. For a round tree ring, choose Circle and enter the diameter.
2. Enter the length and width (or diameter) and the depth you want. Use 3 inches if you are not sure.
3. Choose bags or bulk, enter the bag size and the price, and read the volume, the bag count and the cost.

A mulch calculator is a volume tool for garden beds. It turns the size of a bed and the depth of mulch into the amount of material to buy. Mulch is any layer spread over soil, such as shredded bark, wood chips, pine straw, leaves, compost or stone.

It helps homeowners buying bags at a garden center and anyone ordering bulk mulch by the cubic yard. It stops two costly errors: a second trip because you ran short, and a pile left over because you guessed high.

The calculator measures volume, not weight. It does not choose a mulch type for you, and it does not account for plants, rocks or paths inside the bed. For soil and compost jobs that use the same math, the mulch or topsoil guide compares both materials.

The calculator multiplies the bed area by the depth to get volume, then converts it to the unit you buy in.

1. Area. A rectangle is length x width. A circle is pi x radius squared, where the radius is half the diameter.
2. Depth in the same unit. Inches become feet by dividing by 12. Centimeters become meters by dividing by 100.
3. Volume and conversion. Area x depth gives cubic feet or cubic meters. One cubic yard is 27 cubic feet, so divide cubic feet by 27.
4. Bags and cost. Volume divided by bag size, rounded up to a whole bag, gives the bag count. Price per unit then gives the cost.

The 324 shortcut comes from 27 cubic feet x 12 inches. It means one cubic yard spreads over 324 square feet at 1 inch deep. The University of Florida uses this same rule in its mulch guidance.

Rectangular bed. A bed is 10 ft x 4 ft, so its area is 40 sq ft. At 3 in deep, 40 x 0.25 ft = 10 cu ft. That is 10 / 27 = 0.37 cu yd. With 2 cu ft bags you need exactly 5 bags. At $4.50 each, the cost is $22.50.

Tree ring. A ring 8 ft across has a radius of 4 ft and an area of 50.27 sq ft. At 3 in deep it needs 12.57 cu ft, or 0.47 cu yd. In 2 cu ft bags, that rounds up to 7 bags.

Large yard. A 30 ft x 20 ft area is 600 sq ft. At 3 in deep, 600 x 3 / 324 = 5.56 cu yd. That would be 75 bags of 2 cu ft, so bulk delivery makes more sense.

Metric bed. A 5 m x 2 m bed at 7.5 cm needs 10 x 0.075 = 0.75 cubic m, or 750 L. That is 15 bags of 50 L.

Depth drives the answer more than anything else, because the volume rises in step with it.

Mulch Type and Texture

Penn State Extension advises 2 to 4 inches of organic mulch, but only 1 to 2 inches of fine mulch. Fine material lets less oxygen through to the soil. University of Maryland Extension lists 1 inch for compost and sawdust.

Existing Mulch

Measure what is already there before you top up. The University of Florida says to add more once the layer falls below 2 inches. Topping a 600 sq ft bed up by 1 inch needs only 1.85 cu yd, not 5.56.

Settling

Fresh mulch is fluffy and settles as it breaks down. Florida studies found pine bark kept about two-thirds of its depth after two years, while pine straw settles fast. Many gardeners add a small extra margin for this.

Shape and Slope

Curved beds and slopes hold more surface than a flat rectangle drawn on paper. Split the bed into simple shapes, measure each, and add the volumes.

Trees and New Plantings

Colorado State University Extension suggests mulching the planting area of new trees 4 to 5 inches deep with coarse wood chips. It also says to keep mulch at least 6 inches from the trunk.

Bags suit small beds, and bulk often wins once the job needs more than a cubic yard or two.

Enter both options in the calculator to compare. Put the bag price in Bags mode, then switch to Bulk and enter the price per cubic yard plus any delivery charge spread across the order.

Spring Bed Refresh

Measure each bed, check the depth that remains, and calculate only the top-up. This is where most people overbuy.

New Landscape Beds

A new bed starts at bare soil, so enter the full 3 inch depth. Combine it with the gravel driveway guide if you are also laying stone paths or edging.

Tree Rings and Playgrounds

Choose Circle for trees. The University of Florida suggests a mulched circle at least 8 feet across. For hardscape jobs that need the same area x depth math, such as a slab, see how much concrete for a slab.

1. Mixing Inches and Feet

Multiplying 40 sq ft by 3 gives 120, which reads as 120 cubic feet. The depth must be 0.25 ft, which gives 10 cu ft. The calculator converts the depth for you.

2. Buying Cubic Feet When the Supplier Means Cubic Yards

One cubic yard is 27 cubic feet. Ordering 10 yards when you need 10 cubic feet is 27 times too much.

3. Piling Mulch Too Deep

More is not better. Penn State Extension warns that deep mulch can starve roots of oxygen and keep bark too wet. Maryland Extension notes that plants can decline, and even die, under too much mulch.

4. Volcano Mulching Around Trees

A cone of mulch against a trunk traps moisture and invites rot, pests and rodents. Leave a gap at the base and keep the root flare visible.

5. Ignoring What Is Already There

Old mulch counts toward your depth. Adding a full 3 inches on top of 2 inches gives a 5 inch layer.

6. Rounding Measurements Early

Round only the final bag count. Rounding a 9.6 ft side down to 9 ft loses over 6 percent of the area.

The math is exact for the shapes and depth you enter, so accuracy depends on your tape measure and on how evenly you spread the mulch.

One cubic yard covers 108 square feet at 3 inches deep. It covers 162 square feet at 2 inches and 81 square feet at 4 inches. Divide 324 by your depth in inches to get the figure for any depth.

It takes 13.5 bags of 2 cubic feet to make one cubic yard. With 1.5 cubic foot bags you need 18, and with 3 cubic foot bags you need 9.

Most landscape beds need 2 to 4 inches of organic mulch. Fine mulch, such as compost, works best at 1 to 2 inches because it lets less air reach the soil.

Keep mulch several inches away from the trunk. Penn State suggests 3 to 5 inches for young trees and 8 to 10 inches for mature ones. The root flare should stay visible.

Split it into rectangles and circles, measure each part, and run the calculator for each. Add the volumes together. For a long curved strip, use its average width.

Usually not. Measure the layer that remains and add only enough to bring it back to 2 to 4 inches. The University of Florida suggests a thin new layer once the old one falls below 2 inches.

Bulk is often cheaper per cubic yard once you need more than a yard or two. Delivery fees can erase the saving on small jobs, so compare both totals in the calculator.

Yes, the volume math is the same for any loose material. Use the depth your product recommends. Stone and soil are much heavier, so check the weight limit of your vehicle.

The bed was likely bigger or deeper than measured, or the soil surface was uneven. Low spots take extra mulch, so measure the depth in a few places as you spread.

No. The calculator runs in your browser and nothing is sent to our servers. Anything you choose to Save stays in this browser only.

• Mulching landscape trees: 2 to 4 inch depth, finer mulch thinner, keep off trunks (Penn State Extension).
• Mulching trees and shrubs: depths by mulch type (University of Maryland Extension).
• Choosing and installing mulches: the 324 coverage rule and when to replenish (UF/IFAS Gardening Solutions, University of Florida).
• Mulching trees and shrubs: distance from the trunk (Colorado State University Extension).
• Exact factors for the foot, inch, cubic foot and cubic yard (NIST SP 811, Appendix B.8).