Measure your garden beds to find the square footage

The amount of mulch you need depends on the area you're covering and how deep you want the layer to be. Start by measuring the length and width of each garden bed in feet. If your bed is rectangular, multiply length × width to get square footage. If it's an irregular shape, break it into smaller rectangles, calculate each one, then add them together.

For circular or curved beds, measure the distance across the widest point (the diameter), divide by 2 to get the radius, then use the formula: radius × radius × 3.14. Write down the square footage for each bed so you don't lose track—you'll need these numbers in the next step.

Key Takeaways

  • Measure the length and width of each bed in feet, multiply them together, and add up all the square footages to get your total coverage area.
  • Most garden beds need 2 to 4 inches of mulch; 3 inches is the standard depth that suppresses weeds while letting water through.
  • Divide your total square footage by 100 to find how many cubic yards of mulch to order, using the 3-inch depth as your baseline.
  • Mulch settles and breaks down over time, so order 10 to 15 percent extra to account for settling in the first few weeks.
  • One cubic yard of mulch covers roughly 100 square feet at 3 inches deep, but this varies slightly by mulch type and how densely you pack it.

Decide on the depth you want

Mulch depth matters because it affects how well it suppresses weeds and retains moisture. A layer that's too thin won't block sunlight from reaching weed seeds. A layer that's too thick can trap moisture against the soil and rot plant stems. The standard depth for most garden beds is 3 inches—deep enough to do the job without creating problems.

If you're mulching around trees or shrubs, 3 inches is still appropriate, but keep the mulch a few inches away from the trunk or stem itself. If you're filling in a new bed with poor soil, you might go to 4 inches. If you're topping off a bed you mulched last year, 2 inches is usually enough because the old mulch is still there underneath.

Convert square footage to cubic yards

Mulch is sold by the cubic yard, not by square feet, so you need to convert. The standard rule is that one cubic yard of mulch covers 100 square feet at a depth of 3 inches. To find how many cubic yards you need, divide your total square footage by 100.

If your beds add up to 300 square feet and you want 3 inches of mulch, you need 300 ÷ 100 = 3 cubic yards. If you want 4 inches instead, multiply your cubic yards by 1.33 (because 4 inches is one-third deeper than 3 inches). If you want 2 inches, multiply by 0.67. Write down your final number—this is what you'll order.

Account for settling and compaction

When mulch is first delivered and spread, it sits loosely. Over the first few weeks, it settles and compacts as it gets wet and as you water your plants. This settling can reduce the visible depth by 10 to 15 percent. To account for this, order 10 to 15 percent extra mulch beyond your calculated amount.

If your calculation came to 3 cubic yards, add 0.3 to 0.45 cubic yards (roughly one-third of a yard) to your order. Most suppliers will round to the nearest half-yard anyway, so ordering 3.5 cubic yards instead of 3 is a practical way to handle settling. You can always use leftover mulch next year or in other beds.

Adjust for mulch type and density

The 100 square feet per cubic yard rule assumes standard wood chip mulch at typical density. Some mulch types are heavier or lighter, which affects coverage slightly. Shredded hardwood mulch and bark nuggets are denser and may cover slightly less area per cubic yard—closer to 90 to 95 square feet. Straw and lighter materials may cover slightly more, around 110 to 120 square feet per cubic yard.

If you're using a specialty mulch like cedar chips or cocoa hulls, ask the supplier what coverage they recommend. The difference is usually small enough that it won't throw off your order by more than half a yard, but it's worth knowing. For most home gardeners using standard wood chips, the 100 square feet rule is accurate enough.

Use a straightforward worksheet to organize your measurements

Rather than trying to keep numbers in your head, write them down as you measure. Create a straightforward list with the bed name or location, its length, its width, and the square footage (length × width). Add up all the square footages at the bottom. Then divide by 100 to get cubic yards, multiply by 1.1 or 1.15 to add the settling buffer, and round to the nearest half-yard.

Here's an example: Front bed is 10 feet long and 4 feet wide = 40 square feet. Side bed is 15 feet long and 3 feet wide = 45 square feet. Back bed is 8 feet long and 6 feet wide = 48 square feet. Total = 133 square feet. Divided by 100 = 1.33 cubic yards. Add 15 percent for settling = 1.53 cubic yards. Round to 1.5 or 2 cubic yards depending on how much buffer you want.

Order from a local supplier or garden center

Once you know how many cubic yards you need, contact a local landscape supply company, garden center, or home improvement store. Many suppliers deliver for free or a flat fee if you order a certain amount (often 3 cubic yards or more). Delivery is usually faster and cheaper than trying to haul bags home yourself, especially for larger orders.

When you call or visit, tell the supplier your square footage and desired depth, and they can confirm the cubic yardage. Ask whether the price includes delivery and whether they can spread it for you (some do, for an extra fee). If you're ordering bags instead of bulk, the math is different—a standard 2-cubic-foot bag covers about 8 square feet at 3 inches deep, so divide your square footage by 8 to find how many bags you need.

Frequently Asked Questions

What if my garden bed is an odd shape?

Break it into rectangles or triangles, measure each section separately, calculate the square footage for each, and add them together. For a triangle, use length × width ÷ 2. For a circle, use radius × radius × 3.14. Irregular shapes are just combinations of these basic shapes.

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

No. If the old mulch is still in decent condition, you can spread new mulch on top. Just rake out any clumps or heavily decomposed material, then add 1 to 2 inches of fresh mulch. This is cheaper than removing everything and starting over.

Can I use the 100 square feet per cubic yard rule for all mulch types?

It's a good baseline for standard wood chips. Denser mulches like bark nuggets may cover 90 to 95 square feet per yard, while lighter materials like straw may cover 110 to 120. Ask your supplier what they recommend for the specific type you're buying.

What if I order too much mulch?

You can store it in bags or a pile in a dry spot for next year, use it in other beds, or offer it to a neighbor. Mulch keeps for several months if it stays reasonably dry. Some suppliers will also take back unopened bags or unused bulk mulch for a refund or credit.

Should I measure in inches or centimeters?

Stick with feet and inches—that's what the standard coverage rule uses. If you measure in metric, convert to feet first (1 meter = 3.28 feet). The math is simpler if you stay in the same units throughout.