The mulch calculator turns a bed's length, width and depth into cubic yards and a count of 2-cubic-foot bags, so you can compare a bulk delivery against the bagged price at the store.
It works for rectangular beds. For a circular tree ring, enter the diameter as both length and width and take 79 percent of the result — the area of a circle is π ÷ 4 of the square around it.
How to use it
- 01
Measure the bed in feet
Length and width of the area you will cover. Break an irregular bed into rectangles and add the results; a curved border is close enough to a rectangle once the waste allowance is in.
- 02
Enter the depth in inches
Two to three inches is the usual recommendation for a landscape bed, four is the ceiling, and a fine-textured mulch such as shredded bark should go on at one to two inches. If you are topping up an existing bed, measure what is already there and enter only the difference — mulch settles, but it does not disappear.
- 03
Set a waste allowance
Ten percent by default, for uneven ground and the edges of curved beds. Bulk mulch also settles in the pile between delivery and spreading.
How the math works
Volume
Cubic feet = length × width × (depth ÷ 12); cubic yards = cubic feet ÷ 27. A 20-by-8 bed at 3 inches is 40 cubic feet, or 1.48 cubic yards.
Bags
Bags = cubic feet × (1 + waste) ÷ 2, rounded up, for the 2-cubic-foot bag most retailers stock. The same bed needs 22 bags with ten percent waste. If the store sells 3-cubic-foot bags, divide by 3 instead.
Bulk or bags
One cubic yard is 13.5 bags of 2 cubic feet, or 9 bags of 3. Bulk mulch is usually cheaper per yard above about a yard, but it arrives as a pile on the driveway and has to be moved by wheelbarrow the same weekend. Bags cost more and can wait. Enter the bag price and the bulk price per yard, and the calculator totals both.
Where the number goes wrong
- Piling mulch against tree trunks. A mound around the base — the so-called mulch volcano — holds moisture against bark and invites rot and pests. Keep the trunk flare exposed and taper the mulch outward.
- Going too deep. More than three or four inches suffocates roots and sheds water instead of holding it.
- Measuring the whole bed when only the bare patches need covering.
- Ordering by cubic feet from a supplier that sells by the yard, or the reverse, and getting 27 times too much or too little.
- Expecting mulch alone to stop weeds. It suppresses them; it does not replace pulling the ones already rooted.
Questions people ask
How many bags of mulch are in a cubic yard?
13.5 bags of 2 cubic feet, or 9 bags of 3 cubic feet. The calculator counts the 2-cubic-foot size.
How deep should mulch be?
Two to three inches for a landscape bed and never more than four, pulled back from trunks and stems. Fine-textured mulch goes on at one to two inches; coarse bark can go toward the top of the range.
Should I buy bulk or bagged mulch?
Below about a cubic yard, bags are simpler and not much dearer. Above it, bulk is usually cheaper per yard, provided you can spread a pile the day it arrives.