Measure your garden bed length, width, and desired mulch depth
To find how much mulch you need, you measure three things: how long your garden bed is, how wide it is, and how deep you want the mulch layer. Most people use mulch between 2 and 4 inches deep. Measure in feet, not inches — that makes the math cleaner.
If your bed is an odd shape, break it into rectangles. Measure each rectangle separately, then add the results together. A curved bed can be approximated as a rectangle that's slightly smaller than the actual space — this gives you a reasonable estimate without needing a surveyor.
Key Takeaways
- Multiply length × width × depth (in feet), then divide by 27 to convert cubic feet into cubic yards.
- Measure depth in feet by converting inches: 2 inches = 0.17 feet, 3 inches = 0.25 feet, 4 inches = 0.33 feet.
- One cubic yard of mulch covers roughly 100 to 150 square feet at 2 to 3 inches deep, depending on how densely you spread it.
- Mulch settles over time, so ordering 10 to 15 percent extra accounts for settling and gives you material for top-ups later.
- Measure your beds in feet and use a calculator — the math is straightforward once you have the three numbers.
Convert inches of depth into feet for the formula
The formula works in feet, so you need to convert your depth from inches. Divide the number of inches by 12. A 2-inch layer is 2 ÷ 12 = 0.17 feet. A 3-inch layer is 3 ÷ 12 = 0.25 feet. A 4-inch layer is 4 ÷ 12 = 0.33 feet.
Write these numbers down. You will use them in the next step.
Use the cubic yard formula: length × width × depth ÷ 27
Multiply your bed's length in feet by its width in feet by the depth in feet. That gives you cubic feet. Then divide by 27, because 27 cubic feet equals 1 cubic yard.
Example: A bed that is 10 feet long, 4 feet wide, and 3 inches deep (0.25 feet). The math is: 10 × 4 × 0.25 = 10 cubic feet. Then 10 ÷ 27 = 0.37 cubic yards. You would order 0.5 cubic yards to account for settling.
If you have multiple beds, calculate each one and add them together. A calculator makes this faster and removes the chance of error.
Account for settling and add a buffer
Mulch compacts and settles as it sits in your beds, especially after rain. The layer gets thinner over the first few weeks. Ordering 10 to 15 percent extra gives you material to top up the beds later without needing a second delivery.
If your calculation comes to 5 cubic yards, order 5.5 to 5.75 cubic yards instead. This is also useful if you want to refresh the mulch in other parts of your yard later in the season.
Use the coverage rule of thumb as a check
One cubic yard of mulch covers roughly 100 to 150 square feet at a depth of 2 to 3 inches. This varies based on how densely you spread it and the type of mulch — shredded bark spreads differently than wood chips.
To use this as a check: find your bed's total square footage (length × width), then divide by 100 or 150. If your bed is 200 square feet and you want 3 inches deep, you need between 1.3 and 2 cubic yards. Compare this to your formula result — they should be close. If they are far apart, recheck your measurements.
Measure irregularly shaped beds by breaking them into sections
Not every garden bed is a rectangle. For an L-shaped bed, imagine it as two rectangles joined together. Measure the length and width of each rectangle, calculate the cubic yards for each, then add them.
For a curved or circular bed, measure the longest point across (the diameter) and the widest point perpendicular to that. Treat it as a rectangle slightly smaller than those measurements — this gives you a conservative estimate that accounts for the curves. If your circular bed measures 8 feet across, use 7 feet × 7 feet as your rectangle, which is close enough for mulch ordering.
Order from a landscape supplier or garden center
Once you know your cubic yardage, call a local landscape supplier or garden center and tell them the amount and the type of mulch you want. Suppliers usually deliver in increments of 0.5 cubic yards, so your order will round to the nearest half-yard.
Delivery costs vary by location and distance. Some suppliers have a minimum order (often 2 to 3 cubic yards), while others charge per cubic yard. Asking about delivery before you order prevents surprises. If your order is small, you may find it cheaper to pick up bags of mulch from a garden center instead, though this takes more time and physical effort.
Frequently Asked Questions
What if my garden bed is not a perfect rectangle?
Break it into rectangles or approximate it as one. For a circular bed, measure across the widest point and use that as both length and width. For an L-shape, measure each arm as its own rectangle and add the results. This method gives you a close estimate — mulch suppliers expect some variation.
Should I measure 2, 3, or 4 inches deep?
Two inches is the minimum for weed suppression and moisture retention. Three inches is standard and works well for most gardens. Four inches is thicker than necessary for most purposes and uses more mulch. Check what your plants prefer — some shrubs like deeper mulch, while shallow-rooted plants may prefer 2 inches.
What happens if I order too much mulch?
Extra mulch keeps in a dry place for months. You can use it to refresh beds later in the season as the original layer settles, or spread it in new areas. Ordering slightly extra is better than running short and needing a second delivery.
Do I need to remove old mulch before spreading new mulch?
If the old mulch is still in decent shape, you can spread new mulch on top. If it is matted, moldy, or very thin, rake it out first. Spreading new mulch over old mulch can create a layer that is too thick and may trap moisture against plant stems, which causes rot.
Can I use the same formula for wood chips and shredded bark?
Yes. The cubic yardage is the same regardless of mulch type. The difference is in appearance and how quickly it breaks down — wood chips last longer, while shredded bark breaks down faster and enriches the soil sooner. Both settle at similar rates, so the 10 to 15 percent buffer applies to both.