Measure your garden bed length, width, and desired mulch depth to find the volume you need
The fastest way to know how much mulch to buy is to measure your garden bed in feet, then multiply length × width × depth (in feet), and divide by 27 to convert cubic feet into cubic yards. Most garden centers sell mulch by the cubic yard, so that final number is what you'll order. A standard 2-inch mulch layer—the depth most gardeners use—requires about 1 cubic yard per 160 square feet of bed space.
You do not need to guess or overbuy. A few minutes with a measuring tape and a calculator gives you an exact number, which saves money and prevents the waste of leftover mulch sitting in your yard.
Key Takeaways
- Measure your bed length and width in feet, multiply them together, then multiply by your desired depth in feet (usually 0.17 feet for a 2-inch layer), and divide the result by 27 to get cubic yards.
- A 2-inch mulch depth is standard for most garden beds and flower borders, while tree bases often need 3 to 4 inches.
- If your bed is an irregular shape, break it into rectangles, calculate each one separately, then add the totals together.
- Most garden centers and landscape suppliers sell mulch by the cubic yard, and delivery is often included for orders of 5 cubic yards or more.
Measure bed length and width in feet
Start with a cloth measuring tape or a 25-foot tape measure. Measure the longest edge of your bed from end to end, and write that number down. Then measure the width at the widest point. If your bed is roughly rectangular, those two measurements are all you need.
If your bed is L-shaped, curved, or has an irregular outline, divide it mentally into two or three rectangles. Measure each rectangle separately—length and width—and you'll calculate the volume for each one, then add them together at the end. This takes a few extra minutes but is far more accurate than trying to estimate an odd shape.
Write your measurements on paper or in your phone. Feet and inches are easier to work with than mixed units, so convert everything to decimal feet: 6 inches = 0.5 feet, 3 inches = 0.25 feet, 9 inches = 0.75 feet.
Decide on mulch depth based on bed type
The depth you choose depends on what the mulch is doing. For flower beds and vegetable gardens, a 2-inch layer is standard—deep enough to suppress weeds and hold moisture, but not so deep that it smothers plant stems or prevents water from reaching soil. This is the depth most gardeners use and the one most bag and bulk suppliers assume when they quote coverage rates.
For tree bases and shrub rings, use 3 to 4 inches to protect the soil and regulate temperature around the root zone. Keep mulch a few inches away from the tree trunk itself to prevent rot and pest problems. For pathways or areas where you want heavy weed suppression, 3 inches is reasonable.
Do not exceed 4 inches in most cases. Mulch that is too deep can trap moisture against plant stems, encourage fungal growth, and create habitat for pests. If you are refreshing an existing mulch bed that already has 1 inch of old mulch, add only 1 to 1.5 inches of new mulch rather than the full 2 inches.
Convert depth to decimal feet and calculate volume
Once you know your desired depth in inches, convert it to feet as a decimal. 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.
Now multiply: length (in feet) × width (in feet) × depth (in feet) = cubic feet. For example, a bed that is 10 feet long, 4 feet wide, and you want 2 inches deep: 10 × 4 × 0.17 = 6.8 cubic feet.
If you have multiple beds, calculate each one separately and add the totals. A 10 × 4 bed plus a 6 × 3 bed would be 6.8 cubic feet plus (6 × 3 × 0.17 = 3.06 cubic feet) = 9.86 cubic feet total.
Convert cubic feet to cubic yards for ordering
Garden centers and landscape suppliers sell mulch by the cubic yard, not cubic feet. One cubic yard equals 27 cubic feet. Divide your total cubic feet by 27 to get cubic yards.
Using the example above: 9.86 cubic feet ÷ 27 = 0.37 cubic yards. Most suppliers have a 1-yard minimum, so you would order 1 cubic yard. If your calculation comes to 1.5 cubic yards, order 1.5 or 2 yards depending on whether you want extra for settling or future top-ups.
Mulch settles over time as it breaks down, so it is normal to lose 10 to 15 percent of volume over the first few months. If you want your beds to look full by mid-summer, order slightly more than your calculation suggests—about 10 percent extra is reasonable.
Use a quick reference table for common bed sizes
If math is not your preference, this table shows cubic yards needed for a standard 2-inch mulch depth on rectangular beds:
| Bed Length | Bed Width | Cubic Yards Needed |
|---|---|---|
| 10 feet | 4 feet | 0.25 cubic yards |
| 15 feet | 4 feet | 0.37 cubic yards |
| 20 feet | 4 feet | 0.50 cubic yards |
| 20 feet | 6 feet | 0.74 cubic yards |
| 25 feet | 6 feet | 0.93 cubic yards |
| 30 feet | 8 feet | 1.48 cubic yards |
For depths other than 2 inches, adjust these numbers: multiply by 1.5 for a 3-inch depth, or by 2 for a 4-inch depth. A 20 × 6 bed at 3 inches deep would need 0.74 × 1.5 = 1.11 cubic yards.
Account for settling and future maintenance
Mulch compacts and breaks down as it sits in your beds. Within the first month, you may notice it has settled by half an inch or more, especially if you water heavily or live in a humid climate. By the end of the first year, you will have lost roughly 10 to 15 percent of the original volume.
If you want your beds to look full and well-maintained by mid-summer, order about 10 percent more than your calculation. For a bed that needs 1 cubic yard, order 1.1 cubic yards. For 2 cubic yards, order 2.2 cubic yards. This extra mulch also gives you material to top up beds in the fall or spring without having to buy a full new load.
Keep any leftover mulch in a dry spot—a corner of your yard or under a tarp works well. It will stay usable for at least a year and is handy for refreshing beds or filling in bare spots.
Frequently Asked Questions
Do I need to remove old mulch before adding new mulch?
No, you can add new mulch directly over old mulch if the old layer is still in decent shape. If the old mulch has turned dark and compacted into a thin mat, rake it loose first so water can penetrate. If it smells sour or has visible mold, remove the top inch or two before adding fresh mulch.
What if my bed is circular or has curved edges?
Measure the diameter (the distance across the widest point) and use the formula for a circle: radius squared × 3.14 × depth ÷ 27. For example, a 6-foot-diameter circle at 2 inches deep: (3 × 3) × 3.14 × 0.17 ÷ 27 = 0.17 cubic yards. For irregular curves, break the bed into rectangles and triangles, calculate each, and add them together.
How much does a cubic yard of mulch weigh?
A cubic yard of mulch typically weighs 400 to 600 pounds depending on moisture content and mulch type. Wet mulch weighs more than dry mulch. If you are ordering delivery, the supplier's truck can usually handle 10 to 15 cubic yards, but confirm weight limits with them before ordering a large load.
Can I buy mulch in bags instead of by the yard?
Yes, most garden centers sell mulch in 2 or 3 cubic foot bags. A cubic yard is 27 cubic feet, so you would need nine 3-cubic-foot bags or thirteen 2-cubic-foot bags per yard. Bagged mulch costs more per cubic foot than bulk mulch, but it is useful for small beds or if you do not have room for a delivery truck.
Should I measure mulch depth differently for slopes or raised beds?
For slopes, measure depth at the center of the bed—mulch will naturally slide downhill and thin out on the lower edge. For raised beds, measure the interior dimensions (length and width inside the frame) and use the same depth formula. If your raised bed is only 6 inches tall and you want 2 inches of mulch, you have 4 inches left for soil, which is shallow for most plants.