Measure your garden beds and multiply by depth

To find out how much mulch you need, measure the length and width of each garden bed in feet, multiply those numbers together to get square footage, then multiply by the depth you want in feet. Most people use 2 to 3 inches of mulch. If you want 2 inches, divide your square footage by 162. If you want 3 inches, divide by 108. The result is how many cubic yards of mulch to order.

For example: a bed that is 10 feet long and 4 feet wide is 40 square feet. At 2 inches deep, you divide 40 by 162, which gives you about 0.25 cubic yards. At 3 inches deep, you divide 40 by 108, which gives you about 0.37 cubic yards. Most mulch suppliers sell by the cubic yard, so you would round up and order 1 cubic yard for a single bed that size.

If your beds are an odd shape, break them into rectangles, measure each one separately, add the square footage together, then do the division. A bed shaped like an L is really two rectangles — measure the top part and the side part, add them, then divide by 162 or 108.

Key Takeaways

  • Multiply length times width to get square footage, then divide by 162 for 2-inch depth or 108 for 3-inch depth to find cubic yards needed.
  • Most landscape mulch works best at 2 to 3 inches deep — thinner than that and weeds push through, thicker and it can trap moisture and rot plant stems.
  • Mulch suppliers sell by the cubic yard, and one cubic yard covers about 162 square feet at 2 inches or 108 square feet at 3 inches.
  • Order 10 to 15 percent extra to account for settling and uneven spreading, especially if you are doing the work yourself.
  • Measure each bed separately if they vary in size, add the totals, then order one amount rather than ordering for each bed individually.

Account for settling and spreading unevenness

Mulch settles over time as it breaks down and compacts under rain and foot traffic. Order about 10 to 15 percent more than your calculation shows. If your math says you need 5 cubic yards, order 5.5 to 6 cubic yards instead.

When you spread mulch by hand, it never goes down evenly. Some spots end up thicker, some thinner. Ordering extra gives you material to top up thin areas without running short. If you are hiring someone to spread it, they may charge by the yard delivered rather than by the yard spread, so ask whether the price includes labor or just the material.

Use a depth gauge or ruler to check your work

After you spread mulch, use a ruler or a depth gauge to check that you hit your target depth. Push the ruler straight down into the mulch until it hits soil. Most garden centers sell straightforward plastic depth gauges for a few dollars, or you can use a yardstick marked with tape at 2 or 3 inches.

Check several spots across each bed — near the edges, in the middle, and around plant stems. Mulch should sit an inch or two away from tree trunks and shrub stems to prevent rot and pest damage. If you find thin spots, you have extra material on hand to fill them in.

Adjust your calculation for slopes and raised beds

Sloped beds need more mulch because material slides downhill. Measure the bed as if it were flat, then add 20 to 30 percent extra. A 100-square-foot sloped bed should be treated as 120 to 130 square feet in your calculation.

Raised beds are simpler because the sides hold the mulch in place. Measure the inside length and width, multiply to get square footage, then divide by 162 or 108 as usual. Raised beds often look better with 3 inches of mulch rather than 2, so the division by 108 is common for them.

Know what one cubic yard looks like when it arrives

One cubic yard of mulch is a pile roughly 3 feet long, 3 feet wide, and 3 feet tall. When it is dumped in your driveway or yard, it looks like a lot more material than you might expect. The pile will spread out as you work it into beds, and it compacts as you rake and water it.

If you ordered 5 cubic yards, expect a pile that takes up a space about 15 feet long and 3 feet wide, or a smaller pile stacked higher. Most delivery trucks can dump the pile in one spot, but ask the supplier where they will leave it. If your driveway is narrow or you have limited space, ask whether they can make multiple smaller drops.

Calculate mulch for tree rings and around shrubs

For a circular area around a tree or shrub, measure the radius (the distance from the center to the edge) in feet. Multiply the radius by itself, then multiply by 3.14. That gives you the square footage. Then divide by 162 or 108 as usual.

For example: a tree ring that is 3 feet from the center to the edge has a radius of 3. Multiply 3 by 3 to get 9, then multiply by 3.14 to get about 28 square feet. At 2 inches deep, divide 28 by 162 to get about 0.17 cubic yards. Most people order a half cubic yard for a single tree ring and have material left over for touch-ups.

Frequently Asked Questions

How deep should mulch be?

Two to three inches is the standard depth. Thinner than 2 inches and weeds break through. Thicker than 3 inches and mulch can trap moisture against plant stems, causing rot. Around tree trunks, keep mulch 1 to 2 inches away from the bark.

Do I need to remove old mulch before adding new mulch?

No. If the old mulch is still in decent shape, you can add new mulch on top. If it has broken down into soil-like material, rake it out first. Mulch that is matted down or moldy should be removed and replaced rather than topped off.

What if my beds are irregularly shaped?

Break the bed into rectangles or circles, measure each section separately, add the square footage together, then do your division. Odd shapes always add up to a combination of straightforward shapes.

Can I order mulch in bags instead of by the cubic yard?

Yes. Most bags hold 2 or 3 cubic feet. One cubic yard is 27 cubic feet, so you would need 9 to 13 bags per cubic yard depending on bag size. Bagged mulch costs more per cubic yard but works for small beds or if you do not have space for a bulk delivery.

How long does mulch last before I need to replace it?

Mulch breaks down over one to three years depending on the type and climate. Hardwood mulch lasts longer than softwood. In hot, wet climates it breaks down faster. Plan to add a fresh layer every year or two to maintain the 2 to 3 inch depth.