Mulch Calculator

Mulch comes in bags or in bulk. Bags are labeled by volume: a common size is 2 cu ft, and a smaller 1.5 cu ft bag is sold too. Bulk mulch is sold by the cubic yard, and a cubic yard is 27 cubic feet. The calculator reports both as cubic yards and bags.

How to use this calculator

1. Choose the shape that matches the area. Use rectangle for beds, borders and strips along a fence, ring for a tree ring, circle for a round bed, and triangle for a corner wedge.
2. Enter length and width in feet, or switch to inches for a narrow border. The calculator converts every measure to feet before it works out the volume.
3. Enter the depth you want when the job is finished. Most landscape beds take 2 to 3 inches, so start in that range and adjust from there.
4. For a tree ring, enter the outside diameter and the inside diameter. The inside measure is the open space around the trunk, which stays clear of mulch.
5. If mulch is already down, measure it, then enter only the difference, as the topping up section explains.
6. Compare the bag count with the cubic yards before you shop. Round up when you buy, because a short load leaves a bare patch.

Worked examples

Bags of 2 cu ft mulch for common bed sizes

Number of 2 cu ft bags, exact volume without extra for waste.

Bags or bulk by the yard?

Bags suit a tree ring, a few flower beds or a short border. A cubic yard takes 14 bags of 2 cu ft or 18 bags of 1.5 cu ft, and every bag has to be cut open, lifted and spread by hand.

For a long border, a large bed or a whole yard, bulk mulch delivered by the cubic yard saves a lot of handling. Suppliers often set a minimum order and a delivery fee, so ask before you book, and plan where the pile will go.

How deep should mulch be?

• Most landscape beds do well with 2 to 3 inches, which extension guidance calls sufficient for most applications.
• At the top of that range, a cubic yard covers 108 square feet of bed. Use that as a check against the area you measured.
• A thicker layer costs more, is harder to spread evenly and is not needed for most beds. Stay in the range unless you have a specific reason to go further.
• A thin layer lets weeds and bare soil show through. If you can see soil between the pieces, it is time to add some.
• Ask a local extension office about plant-specific depths, especially around shrubs and young trees.

Keeping mulch off trunks and stems

Mulch should stop short of the trunk. Mulch piled against bark keeps the base of the tree wet and gives pests a place to hide, so pull it back as you spread. The bare center of a tree ring is the area the ring calculation leaves out.

Build a flat, even ring rather than a cone. The same rule applies to shrubs: the stems should sit in the open, not buried in a mound.

Topping up an existing layer

Mulch breaks down, washes away and gets raked off the edges, so an old bed is often thinner than it was. If the soil under the bed has sunk too, fill it with garden soil or a layer of compost before you top up the mulch. Measure before you buy. Push a ruler down through the mulch to the soil in several spots, and take the average.

Subtract that average from the depth you want, and enter the difference as the depth. The Topping up an old bed example uses that difference as its depth. If the existing layer already matches your target, you do not need to buy any.

How do I calculate mulch by hand?

Multiply the length by the width, both in feet, to get square feet. Divide the depth in inches by 12 inches to turn it into feet, then multiply by the square feet to get cubic feet. Divide the cubic feet by 27 cubic feet to get cubic yards.

Common questions