Measure your garden beds to find the square footage

The fastest way to figure out how much mulch you need is to measure the length and width of each garden bed, multiply those numbers together, and add them up. Mulch is sold by volume—cubic yards or cubic feet—so you need to know the area you're covering first.

For a rectangular bed, measure the length in feet and the width in feet, then multiply them. A bed that is 10 feet long and 4 feet wide is 40 square feet. If you have an oddly shaped bed, break it into rectangles, find the square footage of each section, and add them together. For a circular bed, measure across the widest point (the diameter), divide that number by 2 to get the radius, then use the formula: radius × radius × 3.14. A circular bed with a 6-foot diameter has a radius of 3 feet, so 3 × 3 × 3.14 = 28.26 square feet.

Key Takeaways

  • Multiply the length and width of each bed in feet to get square footage, then add all beds together.
  • Most home gardeners spread mulch 2 to 3 inches deep, which is the standard depth for weed control and moisture retention.
  • Divide your total square footage by 324 if you want a 1-inch layer, by 162 for 2 inches, or by 108 for 3 inches to get cubic yards.
  • One cubic yard of mulch covers roughly 324 square feet at 1 inch deep, but coverage varies slightly by mulch type and how densely it settles.

Decide on the depth you want

The depth of mulch you spread changes how much you need. Most home gardeners use 2 to 3 inches because that depth blocks weeds, holds moisture in the soil, and looks finished without looking excessive. One inch is too thin to do much work. Four inches or deeper can trap moisture against plant stems and cause rot.

If you're mulching around trees or shrubs, 2 to 3 inches is still the target. Keep the mulch a few inches away from the trunk or stem so air can reach the base of the plant. If you're refreshing mulch that's already there, you may only need 1 to 2 inches of new mulch on top.

Convert square footage to cubic yards

Once you know your total square footage and the depth you want, use this straightforward math: divide your square footage by a number that depends on depth. At 1 inch deep, divide by 324. At 2 inches deep, divide by 162. At 3 inches deep, divide by 108.

Example: You have 400 square feet of beds and want mulch 2 inches deep. Divide 400 by 162, which gives you 2.47 cubic yards. Round up to 2.5 or 3 cubic yards to account for settling and uneven spreading. If the same bed were 3 inches deep, you'd divide 400 by 108 to get 3.7 cubic yards, so you'd order 4 cubic yards.

These numbers assume standard mulch that settles to a normal density. Shredded hardwood mulch and wood chips settle slightly differently, but the difference is small enough that this method works for both.

Account for settling and waste

Mulch compacts and settles over time, especially in the first few weeks after you spread it. Rain, foot traffic, and the weight of the mulch itself all push it down. Plan to order about 10 percent more than your calculation suggests so you have extra to top off beds after settling.

You'll also lose some mulch to spillage when you're spreading it, especially if you're using a wheelbarrow or spreading by hand. If you're using a landscape contractor or renting a mulch blower, the waste is usually built into their estimate, but if you're doing it yourself, that extra 10 percent covers both settling and the small amount that ends up on paths or driveways.

Use an online calculator if math isn't your strength

Most landscape supply yards and garden centers have mulch calculators on their websites. You enter your square footage and desired depth, and the calculator tells you how many cubic yards to order. Some calculators also let you enter the price per cubic yard so you can see the total cost before you buy.

If you're ordering from a local supplier, call them and give them your square footage and depth. They've done this calculation hundreds of times and can tell you the cubic yardage in under a minute. Many suppliers will also adjust the number slightly based on the type of mulch you're ordering, since different mulches settle at different rates.

Order slightly more if you're unsure about coverage

It's easier to use leftover mulch than to run short and have to order again. Most suppliers charge a delivery fee, so ordering an extra half cubic yard is cheaper than paying to deliver a second small order. You can always use extra mulch in other parts of your yard, or keep it in a pile for next year's touch-ups.

If you're buying mulch in bags rather than by the cubic yard, the math is different. A standard bag of mulch is 2 cubic feet. One cubic yard equals 27 cubic feet, so you need about 13 to 14 bags per cubic yard. For 3 cubic yards, you'd need roughly 40 to 42 bags. Bagged mulch costs more per cubic yard than bulk mulch, but it's easier to transport if you don't have a truck.

Frequently Asked Questions

How many bags of mulch do I need for 100 square feet?

At 2 inches deep, you need about 0.62 cubic yards, which is roughly 8 to 9 bags of standard 2-cubic-foot mulch bags. At 3 inches deep, you need about 0.93 cubic yards, or 12 to 13 bags. Most people buy a few extra bags to account for settling.

Does mulch type change how much I need to order?

Not significantly. Shredded hardwood, wood chips, and bark mulch all settle to roughly the same density. Dyed mulch and colored mulch may compact slightly differently, but the difference is small enough that you can use the same calculation. Ask your supplier if they have specific guidance for the exact product you're buying.

What if my beds are already mulched and I just want to refresh the top?

Measure the same way, but plan for only 1 to 2 inches of new mulch instead of the full 2 to 3 inches. This tops off the existing layer without making it too deep. Divide your square footage by 324 for 1 inch or by 162 for 2 inches.

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

Yes. Wood chips and shredded mulch settle at similar rates, so the cubic yardage calculation is the same. Wood chips may look larger and fluffier when first spread, but they compact to roughly the same depth as shredded mulch within a few weeks.

How do I measure a curved or irregular garden bed?

Break it into smaller shapes. Measure the longest straight section as a rectangle, then measure any curved sections separately. For a gentle curve, treat it as a rectangle and measure the average length and width. For a more complex shape, sketch it on graph paper and count the squares, or take a photo and use a landscape design app to estimate the area.