Measure your garden beds and multiply by depth to find cubic yards

The amount of mulch you need depends on three things: the length and width of your beds, how deep you want the mulch to be, and whether you're measuring in square feet or cubic yards. Most suppliers sell mulch by the cubic yard, so you'll convert your bed measurements to that unit. The math is straightforward—length times width times depth—but getting the measurements right is what matters.

Start by measuring the length and width of each bed in feet. If a bed is oddly shaped, break it into rectangles, measure each one, and add the totals together. Write these numbers down. Then decide how thick you want your mulch layer. Most gardeners use 2 to 3 inches; 2 inches suppresses weeds and retains moisture without piling up too much, while 3 inches gives more weed control in high-traffic beds. Thinner than 2 inches and you won't get much benefit. Thicker than 4 inches and you risk trapping moisture against plant stems, which can rot them.

Key Takeaways

  • Measure each bed's length and width in feet, then multiply by your desired depth in inches (usually 2 to 3 inches) to get cubic feet.
  • Convert cubic feet to cubic yards by dividing by 27, since one cubic yard contains 27 cubic feet.
  • Round up to the nearest half cubic yard when ordering, because mulch settles and you'll need extra to top off beds after a few months.
  • Mulch sold in bags typically contains 2 to 3 cubic feet per bag, so a 3-cubic-yard order equals roughly 30 to 45 bags depending on bag size.
  • Measure twice and order once—it's cheaper to buy a little extra than to place a second order for a small amount.

Convert cubic feet to cubic yards using the 27-foot rule

Once you have your length, width, and depth in feet, multiply them together to get cubic feet. For example, a bed that is 10 feet long, 4 feet wide, and 0.17 feet deep (2 inches) equals 6.8 cubic feet. To convert to cubic yards, divide by 27. That same bed needs about 0.25 cubic yards of mulch.

If you have multiple beds, do this calculation for each one and add them together. A typical suburban yard with three or four beds might need 1 to 3 cubic yards total. A larger landscape with many beds or a vegetable garden can easily need 5 to 10 cubic yards. Keep a running total as you measure.

Account for settling and order a little extra

Mulch compacts and settles over time, especially in the first few weeks after you spread it. Rain, foot traffic, and decomposition all compress the layer. This means a 3-inch layer will drop to about 2.5 inches within a month or two. To keep your beds looking full and maintaining weed suppression, order about 10 to 15 percent more than your calculation shows.

If your math comes to 2 cubic yards, order 2.5. If it comes to 5 cubic yards, order 5.5 or 6. This extra mulch also gives you material to top off beds later in the season without having to buy more. Mulch suppliers are used to this and won't think twice about an order for 2.5 cubic yards instead of a round number.

Decide between bulk delivery and bagged mulch

Bulk mulch is cheaper per cubic yard but requires a delivery truck and a place to dump it. Bagged mulch costs more but works if you have a small order, limited space, or no driveway access. One cubic yard of bulk mulch typically costs less than buying 30 bags, but you'll need to spread it yourself and have somewhere to store it temporarily.

If you're ordering bagged mulch, remember that bag sizes vary. A standard bag holds 2 to 3 cubic feet. Divide your total cubic yards by 0.1 (for 3-cubic-foot bags) or 0.15 (for 2-cubic-foot bags) to find how many bags you need. A 3-cubic-yard order equals about 30 to 45 bags depending on the bag size your supplier carries. Check the bag label before ordering to know exactly what you're getting.

Use a straightforward worksheet to organize your measurements

Write down each bed's dimensions in a table so you don't lose track. Include the length, width, desired depth in inches, and the cubic feet calculation for each bed. Add a final row for your total cubic feet, then divide by 27 to get cubic yards. This takes five minutes and prevents mistakes.

If you're ordering from a local supplier, bring this worksheet with you or call ahead with the total. Many suppliers will help you round up or suggest adjustments based on their experience with your area's soil type. Some mulches settle faster than others, so a supplier who knows your region can give you better information than a general rule.

Account for different mulch types and their coverage

Most mulches—wood chips, shredded bark, compost blends—cover at roughly the same rate by volume. However, some mulches are denser or fluffier than others. Hardwood mulch is denser and compacts more than softwood chips. Colored mulch (dyed wood) is often more densely packed in bags than natural mulch. These differences are small enough that your cubic yard calculation still works, but they mean a 3-inch layer of hardwood mulch will settle faster than 3 inches of pine chips.

If you're using a specialty mulch like rubber or stone, check with the supplier about coverage rates, as these materials don't compress the same way wood does. For standard wood-based mulches, your calculation holds regardless of type.

Frequently Asked Questions

What if my garden bed is circular or has curved edges?

Measure the longest point across the circle (the diameter) and the widest point perpendicular to that. Multiply those two numbers and divide by 4 to get the approximate area. Then multiply by your depth in feet and divide by 27 for cubic yards. This gives you a close estimate. For very irregular shapes, break them into rectangles and triangles, calculate each, and add them together.

How deep should mulch be around trees?

Use the same 2 to 3 inches as you would for garden beds, but keep mulch 3 to 4 inches away from the tree trunk itself. Mulch piled against the trunk can trap moisture and cause rot or pest damage. Spread it in a ring around the tree, leaving a clear circle at the base.

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

If your old mulch is still in decent shape and not matted down, you can add new mulch on top. However, if it's compacted, moldy, or more than 4 inches deep already, rake it out first. Adding new mulch to a thick, settled layer can create a barrier that sheds water instead of absorbing it.

Can I use the same calculation for wood chips as for shredded mulch?

Yes. Both are sold by the cubic yard and cover at the same rate. Wood chips are chunkier and may settle slightly less than shredded mulch, but the difference is small enough that your calculation works for both. The main difference is appearance and how quickly they break down, not coverage.

What if I order too much mulch?

Extra mulch keeps in a dry spot for months. You can use it to top off beds later in the season, add it to new beds you create, or offer it to a neighbor. Mulch doesn't go bad if it stays dry, so having a little extra is never wasted.