Measure Your Garden Area and Decide on Mulch Depth
To find out how many yards of mulch you need, you must know two things: the square footage of the area you are covering, and how deep you want the mulch layer. Most landscaping uses mulch between 2 and 4 inches deep. A 2-inch layer works for annual flower beds and areas that get regular maintenance. A 3-inch layer is standard for shrub beds and areas around trees. A 4-inch layer suits heavy-traffic areas or places where you want mulch to last longer before it breaks down.
Start by measuring the length and width of each bed or area in feet. If your bed is rectangular, multiply length times width. If it is irregular, break it into smaller rectangles, measure each one, and add them together. Write down the total square footage for each separate area—you may want different mulch depths in different spots, and calculating them separately makes the math clearer.
Key Takeaways
- Measure your garden bed in square feet, then multiply by the depth you want (in inches) and divide by 324 to get cubic yards.
- A 2-inch depth works for flower beds, 3 inches for shrub beds, and 4 inches for high-traffic areas or longer-lasting coverage.
- One cubic yard of mulch covers roughly 162 square feet at 2 inches deep, 108 square feet at 3 inches, or 81 square feet at 4 inches.
- Most mulch is sold by the cubic yard, and delivery minimums vary—some suppliers require a 3-yard minimum, others sell smaller amounts.
- Order 10 to 15 percent extra to account for settling and uneven ground, especially if your beds have slopes or low spots.
Use the Square Footage-to-Cubic-Yard Formula
Once you have your square footage and chosen your depth, use this formula: square footage × depth in inches ÷ 324 = cubic yards needed. The number 324 is the constant that converts square feet and inches into cubic yards.
Example: You have a flower bed that is 20 feet long and 5 feet wide (100 square feet), and you want 2 inches of mulch. The math is 100 × 2 ÷ 324 = 0.62 cubic yards. You would order 1 cubic yard, since most suppliers do not sell partial yards. Another example: a shrub bed of 200 square feet at 3 inches deep is 200 × 3 ÷ 324 = 1.85 cubic yards, so you would order 2 cubic yards.
Quick Reference: Coverage by Depth
If you prefer not to do the math, use this quick reference. One cubic yard of mulch covers:
| Depth | Square Footage Covered |
|---|---|
| 2 inches | 162 square feet |
| 3 inches | 108 square feet |
| 4 inches | 81 square feet |
To use this table, divide your total square footage by the number in the right column that matches your chosen depth. If you have 300 square feet and want 3 inches of mulch, divide 300 by 108 to get 2.78 cubic yards—round up to 3 cubic yards.
Account for Settling and Uneven Ground
Mulch settles over time as it breaks down and compacts, especially during the first few weeks after you spread it. It also fills low spots and slopes unevenly. Most landscapers add 10 to 15 percent extra to their calculation to handle this settling and to avoid running short partway through the job.
If your calculation comes to 5 cubic yards, ordering 5.5 to 6 cubic yards gives you a buffer. This is especially important if your beds have slopes, tree roots, or uneven ground. It is easier to have a small pile left over than to place a second order and wait for delivery.
Check Your Supplier's Minimum Order and Delivery
Mulch is sold by the cubic yard, but suppliers have different minimums. Some will deliver as little as 1 cubic yard, while others require a 3-yard or 5-yard minimum. A few sell bagged mulch in smaller quantities—typically 2 or 3 cubic feet per bag—if you need less than a yard or want to avoid delivery fees.
Call your local landscape supply company or garden center and ask what they have in stock, what the minimum order is, and whether delivery is included or costs extra. Delivery fees vary widely depending on distance and the supplier's route. If you are ordering a small amount, bagged mulch from a garden center may cost less than paying a delivery fee on a partial cubic yard.
Measure Irregular Shapes Correctly
Not every garden bed is a perfect rectangle. For curved or L-shaped beds, divide the area into smaller rectangles, measure each one, and add the totals. For a circular bed, measure the radius (the distance from the center to the edge), then use the formula: radius × radius × 3.14 = square footage.
If you have a bed with a radius of 5 feet, the math is 5 × 5 × 3.14 = 78.5 square feet. Then plug that into your depth formula as usual. For very irregular shapes, sketch the bed on graph paper and count the squares, or use a measuring wheel if you have one. The goal is to get as close as you can—being off by 10 or 20 square feet usually does not matter much, since you are rounding up to the nearest yard anyway.
Frequently Asked Questions
How much does one cubic yard of mulch weigh?
Most mulch weighs between 400 and 800 pounds per cubic yard, depending on the type and moisture content. Hardwood mulch is heavier than pine, and freshly delivered mulch is heavier than dry mulch. If you are ordering a large amount, ask your supplier for the weight so you know whether your vehicle or equipment can handle it.
Can I use the same calculation for wood chips or bark?
Yes. Wood chips, bark, and shredded hardwood mulch all use the same square footage and depth formula. The coverage rates are nearly identical. The main difference is how long they last—bark breaks down slower than shredded hardwood, so a 3-inch layer of bark may last longer than 3 inches of hardwood mulch.
What if I want different depths in different parts of my garden?
Calculate each area separately using the formula, then add the cubic yards together. For example, if you want 2 inches in a 100-square-foot flower bed and 4 inches in a 150-square-foot shrub area, calculate both and order the total. This approach also helps you see which areas use the most mulch.
Should I measure before or after removing old mulch?
Measure the bare soil after you remove the old mulch. This gives you the true size of the area you are covering. If you measure over old mulch, you may overestimate, especially if the old layer is uneven or has settled into low spots.
How often do I need to add more mulch?
Mulch breaks down over time, typically losing about half its depth per year depending on the type and climate. Most people add a fresh 1 to 2-inch layer every year or every other year to maintain the original depth and appearance. You do not usually need to remove the old mulch—new mulch goes right on top.