Measure your garden beds in square feet, then divide by the depth you want
To find how many yards of mulch to buy, you need three numbers: the length of your bed in feet, the width in feet, and how deep you want the mulch layer in inches. Multiply length times width to get square feet. Then use a straightforward formula: square feet divided by 324 equals cubic yards. That number 324 comes from the fact that one cubic yard covers 324 square feet at a depth of one inch.
If you want mulch deeper than one inch — say, two or three inches — multiply your square footage by the depth first, then divide by 324. For example, a 100-square-foot bed covered two inches deep needs (100 × 2) ÷ 324 = 0.62 cubic yards. Most landscapers recommend two to three inches as the standard depth for weed suppression and moisture retention.
Key Takeaways
- Measure the length and width of each bed in feet, then multiply them together to get square feet.
- One cubic yard of mulch covers 324 square feet at one inch deep, 162 square feet at two inches deep, and 108 square feet at three inches deep.
- For beds deeper than one inch, multiply square feet by the desired depth in inches, then divide the result by 324.
- Round up to the nearest half yard when you order, because mulch settles and you will need extra to top off beds after a few months.
Work through each bed separately, then add them together
If your yard has more than one garden bed, calculate each one on its own, then add the totals. A front bed that is 10 feet long and 4 feet wide is 40 square feet. A side bed that is 15 feet long and 3 feet wide is 45 square feet. Together that is 85 square feet. At two inches deep, you need (85 × 2) ÷ 324 = 0.52 cubic yards.
For oddly shaped beds — circles, triangles, or curved edges — break them into simpler shapes. A circular bed 8 feet across has a radius of 4 feet. The area is 3.14 × 4 × 4 = about 50 square feet. A triangular bed with a base of 6 feet and a height of 8 feet is (6 × 8) ÷ 2 = 24 square feet. Add these to your other beds before dividing by 324.
Account for settling and choose your depth based on purpose
Mulch compacts over time, especially after rain and as it breaks down. Most landscapers add 10 to 15 percent extra to their order to account for this settling. If your calculation comes to 2.5 cubic yards, ordering 3 cubic yards is safer. You will use the extra to top off beds in late spring or early fall.
The depth you choose depends on what you are trying to do. One inch is the minimum for light weed suppression in established beds. Two inches is the standard for new beds and for suppressing perennial weeds. Three inches is appropriate for areas with heavy foot traffic or where you want maximum moisture retention in dry climates. Do not go deeper than four inches, because mulch that thick can trap moisture against the soil and rot plant crowns.
Use a straightforward table to avoid math mistakes
| Square Feet | 1 Inch Deep | 2 Inches Deep | 3 Inches Deep |
|---|---|---|---|
| 100 | 0.31 yards | 0.62 yards | 0.93 yards |
| 200 | 0.62 yards | 1.23 yards | 1.85 yards |
| 300 | 0.93 yards | 1.85 yards | 2.78 yards |
| 400 | 1.23 yards | 2.47 yards | 3.70 yards |
| 500 | 1.54 yards | 3.09 yards | 4.63 yards |
If your beds add up to a square footage in this table, you can read the answer directly without doing the division. If your total is between two rows — say, 250 square feet — estimate halfway between the two nearest numbers.
Measure beds with a tape measure or by pacing
For straight edges, a 25-foot or 50-foot tape measure is fastest. Stretch it along the length of the bed, write down the number, then measure the width the same way. For curved beds, lay a rope along the edge, mark where it starts and ends, then measure the rope with your tape.
If you do not have a tape measure, you can pace off the distance. Most adults cover about 3 feet per step at a normal pace. Count your steps along the length and width, multiply by 3, and you have a rough measurement. This method is less precise but works well enough for a ballpark figure.
Order mulch in bulk if you need more than two cubic yards
Bags of mulch sold at garden centers are usually 2 or 3 cubic feet each. A cubic yard is 27 cubic feet, so one yard needs nine 3-cubic-foot bags or thirteen 2-cubic-foot bags. If you need 3 cubic yards or more, ordering from a landscape supply company by the yard is cheaper per cubic foot and saves you the work of carrying bags.
When you call a supplier, tell them your total in cubic yards and ask whether they deliver. Most will charge a delivery fee but will spread the mulch in your beds for an additional cost. That service is worth considering if you have a large order or physical limitations that make spreading difficult.
Frequently Asked Questions
Do I need to measure the depth of mulch I already have?
Only if you are topping off an existing bed. Measure the current depth with a ruler or stick pushed into the mulch. If it is still two inches or deeper, you may only need to add half an inch to a full inch. If it is less than one inch, treat it as a fresh bed and calculate for your target depth.
What if my beds are not rectangular?
Break the shape into rectangles, triangles, or circles, calculate each piece, and add them together. For a bed shaped like an L, split it into two rectangles. For a curved edge, approximate it as a straight line or use the rope method described above.
Should I subtract the space taken up by plants?
No. Mulch settles around plants and fills gaps, so you need the full square footage. Subtracting plant space leads to ordering too little and ending up with thin coverage that does not suppress weeds or retain moisture.
How often do I need to add more mulch?
Most mulch breaks down and compacts enough to need topping off once a year, usually in spring. If you use a dyed mulch or cedar, it may last longer. If you use shredded hardwood, you may need to add more by midsummer in hot climates.
Can I use the same calculation for wood chips or bark?
Yes. The coverage rate of 324 square feet per cubic yard at one inch deep applies to any mulch material — shredded hardwood, cedar, pine, wood chips, or bark. The only difference is how quickly it breaks down and how often you need to refresh it.