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

The amount of mulch you need depends on three things: the length and width of the area you're covering, how deep you want the mulch to be, and what unit your supplier sells in. Most garden centers sell mulch by the cubic yard, though some sell by the bag. The math is straightforward: find your square footage, decide on depth, convert to cubic yards, and order.

Start by measuring the length and width of each bed in feet. If a bed is irregularly shaped, break it into rectangles, measure each one, and add the totals. Write down the square footage for each bed so you don't have to remeasure later.

Next, decide how deep you want the mulch. Most landscapers recommend 2 to 3 inches for ornamental beds and around tree bases. If you're covering bare soil to suppress weeds, 3 inches works better than 2. If you're refreshing an existing mulch layer that's already partially decomposed, 1 to 2 inches of fresh mulch on top is usually enough.

Key Takeaways

  • Multiply your bed's length by width to get square footage, then use that number with your chosen depth to calculate cubic yards.
  • A depth of 2 to 3 inches is standard for most garden beds; go deeper if you're starting from bare soil or fighting heavy weeds.
  • One cubic yard of mulch covers roughly 100 to 150 square feet at 2 inches deep, depending on how densely you spread it.
  • Suppliers sell mulch by the cubic yard or by the bag; bags are convenient for small areas but cost more per volume than bulk delivery.
  • Order 10 to 15 percent extra to account for settling and uneven spreading, especially if you're new to the task.

Convert square footage and depth to cubic yards

Once you have your square footage and depth, use this formula: (square footage × depth in inches) ÷ 324 = cubic yards. The number 324 is the conversion factor that accounts for the difference between square feet and cubic yards.

Here's a worked example. Say you have a bed that's 10 feet long and 4 feet wide, and you want the mulch 3 inches deep. Multiply 10 × 4 to get 40 square feet. Then multiply 40 × 3 to get 120. Divide 120 by 324 to get 0.37 cubic yards. Round up to 0.5 cubic yards, or ask your supplier if they have a minimum order.

If you have multiple beds, do this calculation for each one and add them together. A bed that's 20 feet long and 3 feet wide at 2 inches deep is 60 square feet × 2 inches ÷ 324, which equals 0.37 cubic yards. Add that to your other beds to get your total order.

Use the coverage rule of thumb if you don't want to calculate

One cubic yard of mulch covers roughly 100 to 150 square feet at a depth of 2 inches. At 3 inches deep, one cubic yard covers about 80 to 100 square feet. These numbers assume you're spreading the mulch evenly and not packing it down too hard.

If you have 200 square feet of beds and want 2-inch coverage, divide 200 by 100 to get 2 cubic yards. If you want 3-inch coverage, divide 200 by 100 to get 2 cubic yards, then add 25 percent more, which brings you to 2.5 cubic yards. This method is faster than the formula and close enough for most home gardens.

The range (100 to 150 square feet per cubic yard) exists because mulch density varies. Shredded hardwood mulch is denser than pine bark, and freshly delivered mulch is fluffier than mulch that's been sitting in a pile for weeks. When you call your supplier, ask what type of mulch they have and whether it's freshly ground or aged.

Decide between bulk delivery and bagged mulch

Bulk mulch is cheaper per cubic yard but requires a delivery truck and space to unload. A cubic yard of bulk mulch typically costs between $25 and $50, depending on the type and your location. Bagged mulch costs more per volume — usually $3 to $8 per bag — but you can buy exactly what you need and spread it yourself over time.

A standard mulch bag holds 2 to 3 cubic feet, which means you need roughly 9 to 13 bags to equal one cubic yard. For a small bed under 100 square feet, bags make sense. For anything larger, bulk is more economical. If you're ordering bulk, ask whether the supplier includes delivery in the quoted price or charges separately.

Some suppliers offer a middle option: they deliver a pile to your driveway and you spread it yourself. This costs less than having them spread it but more than picking up bags yourself. If your back or knees are a concern, paying for delivery and spreading is worth the cost.

Account for settling and uneven spreading

Mulch settles as it decomposes and as you water your beds. Order 10 to 15 percent extra to account for this. If your calculation comes to 5 cubic yards, order 5.5 to 5.75 cubic yards instead. This extra amount also gives you a buffer if you spread unevenly or if some areas need deeper coverage than others.

When you spread the mulch, use a rake to distribute it evenly. Don't pile it against the base of trees or shrubs — leave 2 to 3 inches of space between the mulch and the stem to prevent rot and pest problems. This spacing doesn't change your calculation, but it does mean some of your mulch will go into the gaps around plants rather than covering bare soil.

Adjust your order for existing mulch and soil type

If you already have mulch in your beds, you may not need a full new layer. Measure the depth of what's there. If it's still 1 to 2 inches thick and not heavily decomposed, add just 1 inch of fresh mulch on top. If it's thin or mostly broken down, treat it as bare soil and order for full depth.

Soil type also affects how much mulch you need. Clay soil holds moisture well, so 2 inches of mulch is usually enough. Sandy soil drains quickly, so 3 inches helps retain water longer. If you're in a dry climate or have sandy beds, lean toward the deeper end of the range.

Frequently Asked Questions

Can I use the same mulch calculation for wood chips and bark mulch?

The formula works for any mulch type, but density varies. Shredded hardwood is denser than pine bark, so one cubic yard of hardwood covers slightly less area. Ask your supplier what type they stock and whether they've measured coverage for that specific product. Most will give you a coverage estimate based on what they sell.

What if my garden bed is circular or oddly shaped?

For a circle, measure the radius (distance from center to edge) and use the formula: 3.14 × radius squared = square footage. For irregular shapes, break them into rectangles and triangles, calculate each one, and add them together. If the shape is too complex, sketch it on graph paper and count the squares.

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

No. If the old mulch is still mostly intact and not heavily decomposed, you can rake it smooth and add fresh mulch on top. If it's mostly broken down into soil, remove it or work it into the top inch of soil, then add new mulch. Removing old mulch is extra work and usually unnecessary unless it's compacted or moldy.

How much mulch do I need if I'm covering a large area with no existing beds?

Measure the length and width of the area, calculate square footage, and use your chosen depth (2 to 3 inches for new areas) with the formula or the coverage rule. If you're creating a new bed from scratch, 3 inches is better than 2 because it suppresses more weeds and breaks down more slowly.

Should I order more mulch if I'm spreading it myself versus having someone else do it?

Order the same amount either way. The difference is in how densely it gets packed. If you spread it loosely, it may look fuller but will settle faster. If someone spreads it professionally, they'll pack it more firmly and it will last longer. Either way, the volume you need is the same.