Measure your garden beds to find the square footage
The first step is to measure the area you want to cover. Use a tape measure to find the length and width of each bed in feet. If your bed is rectangular, multiply length by width. If it's an irregular shape, break it into rectangles, measure each one separately, and add the totals together.
For circular beds, measure the distance across the center (the diameter), divide it by two to get the radius, then use the formula: radius × radius × 3.14. Write down the square footage for each bed so you don't forget.
If you have multiple beds, add all the square footages together to get your total coverage area. This number is what you'll use for every calculation that follows.
Key Takeaways
- Measure the length and width of each bed in feet, multiply them together, and add all the results to find your total square footage.
- Most homeowners use mulch 2 to 3 inches deep, which requires 0.6 to 1 cubic yard per 100 square feet.
- Divide your total square footage by 100, then multiply by the cubic yards needed for your chosen depth to find how much mulch to buy.
- Mulch is sold by the cubic yard at garden centers and landscape suppliers, and delivery is often available for larger orders.
- Buy 10 to 15 percent extra to account for settling and uneven process.
Decide on your mulch depth
Mulch depth affects both how much you need to buy and how well it works. A depth of 2 to 3 inches is standard for most garden beds—it suppresses weeds, holds moisture, and breaks down at a reasonable rate. Shallower mulch (1 to 2 inches) works for tight budgets but needs refreshing more often. Deeper mulch (4 inches or more) is overkill for most situations and can trap moisture against plant stems.
Write down your chosen depth. This is the second number you need for the calculation.
Convert square footage to cubic yards using a straightforward formula
Mulch is sold by the cubic yard, not by square feet. One cubic yard covers roughly 100 square feet at a depth of 3 inches. Here's how to convert:
Divide your total square footage by 100. Then multiply the result by the number of cubic yards needed for your depth. At 2 inches deep, use 0.6 cubic yards per 100 square feet. At 3 inches deep, use 1 cubic yard per 100 square feet. At 4 inches deep, use 1.3 cubic yards per 100 square feet.
Example: You have 500 square feet of beds and want 3 inches of mulch. Divide 500 by 100 to get 5. Multiply 5 by 1 cubic yard. You need 5 cubic yards.
Another example: You have 300 square feet and want 2 inches deep. Divide 300 by 100 to get 3. Multiply 3 by 0.6. You need 1.8 cubic yards, which you'd round up to 2 cubic yards when ordering.
Account for settling and uneven ground
Mulch settles over time as it breaks down and compacts, especially in the first few weeks. It also sits unevenly on sloped or bumpy ground. To avoid running short, add 10 to 15 percent to your final number.
If your calculation came to 5 cubic yards, add 0.5 to 0.75 cubic yards and order 5.5 to 5.75 cubic yards. Most suppliers will round to the nearest half or whole yard, so order 6 cubic yards in this case. It's better to have a small pile left over than to fall short and have to make a second trip.
Where to buy mulch and what to expect
Garden centers, landscape supply yards, and some home improvement stores sell mulch by the cubic yard. Prices vary widely depending on mulch type (wood chips, shredded bark, colored mulch, cedar) and your location. Call ahead or check online to confirm they have your preferred type in stock and what the current price is.
Many suppliers offer delivery for orders of 5 cubic yards or more, though delivery fees vary. If you're buying a smaller amount, you can usually load it yourself into a truck or trailer. Mulch is heavy—one cubic yard weighs roughly 400 to 600 pounds depending on moisture content—so plan for that if you're transporting it yourself.
Use a quick reference table for common bed sizes
| Bed Size (sq ft) | Cubic Yards at 2 inches | Cubic Yards at 3 inches | Cubic Yards at 4 inches |
|---|---|---|---|
| 100 | 0.6 | 1 | 1.3 |
| 200 | 1.2 | 2 | 2.6 |
| 300 | 1.8 | 3 | 3.9 |
| 500 | 3 | 5 | 6.5 |
| 1000 | 6 | 10 | 13 |
If your bed size matches one of these common sizes, you can read the cubic yards directly from the table without doing the math. If your bed is between two sizes, estimate by splitting the difference.
Frequently Asked Questions
Do I need to remove old mulch before adding new mulch?
Not always. If the old mulch is still in decent shape and not compacted into a hard mat, you can add new mulch on top. If it's broken down into soil-like material or is moldy, rake it out first. Mixing old and new is fine if the old layer is less than an inch thick.
What if my beds are oddly shaped or have trees and shrubs in them?
Measure around obstacles by breaking the bed into smaller rectangles and circles, measuring each section, and adding them together. Subtract the square footage of tree trunks and large shrub bases where you won't explore mulch. The goal is to measure only the area that will actually be covered.
Can I use the same calculation for wood chips versus shredded bark?
Yes. Both are sold by the cubic yard and cover roughly the same area at the same depth. Colored mulch and dyed mulch follow the same math. The type you choose affects appearance and how long it lasts, but not how much volume you need.
What if I want mulch deeper than 4 inches?
Very deep mulch (5+ inches) can trap moisture and create conditions for rot near plant stems. If you want extra coverage for weed suppression, lay landscape fabric under 2 to 3 inches of mulch instead of piling mulch deeper. This works better and costs less.
How often do I need to recalculate and add more mulch?
Mulch breaks down over one to three years depending on type and climate. When it settles to 1 inch or less, add a fresh 1 to 2 inches on top. You don't need to remove the old layer—just top it off. Recalculate using the same method each time.