How to measure garden beds for mulch
- Rectangles: measure the length and width in feet. Split L-shaped beds into two rectangles.
- Circles: measure straight across the widest point for the diameter.
- Triangles: measure the base and the height at a right angle to it.
- Tree rings: measure the outer diameter, and the bare circle you will leave around the trunk.
- Curved beds: approximate them with a mix of rectangles and circles. Small errors even out across a whole yard.
How the mulch is calculated
Depth to add = target depth − existing depth
Cubic feet = area in square feet × depth in inches ÷ 12
Cubic yards = cubic feet ÷ 27
Bags = cubic feet ÷ bag size, rounded up
The bulk figure is rounded up to the next half cubic yard. Ask your supplier for their minimum order and how they sell part yards.
Worked example
Two beds of 20 by 4 feet and 12 by 3 feet, plus a 6 foot tree ring with a 1 foot bare circle at the trunk, add up to 143.5 square feet. At 3 inches deep that is 143.5 × 3 ÷ 12 = 35.9 cubic feet, or 1.33 cubic yards. In 2 cubic foot bags you need 18 bags. A bulk order would be 1.5 cubic yards.
How far does mulch go?
| Depth | Sq ft per cubic yard | Sq ft per 2 cu ft bag |
|---|---|---|
| 1 in | 324 | 24 |
| 2 in | 162 | 12 |
| 3 in | 108 | 8 |
| 4 in | 81 | 6 |
Choosing a depth
University extension services recommend 2 to 4 inches of organic mulch. That is enough to hold moisture and block weeds without smothering roots. Use the low end for fine, double-shredded mulch, which packs down more, and the high end for coarse bark or wood chips. Keep a bare ring around tree trunks and shrub stems: University of Illinois Extension names mulch piled against the trunk as a common cause of tree decline.
Frequently asked questions
How many bags of mulch make a cubic yard?
A cubic yard is 27 cubic feet. That is 13.5 bags of 2 cubic feet, 18 bags of 1.5 cubic feet or 9 bags of 3 cubic feet.
How much area does a cubic yard of mulch cover?
At 3 inches deep, one cubic yard covers 108 square feet. At 2 inches it covers 162 square feet, and at 4 inches 81 square feet. The table on this page lists the coverage for each depth.
How deep should mulch be?
Penn State Extension and University of Illinois Extension both recommend 2 to 4 inches of organic mulch. Use 1 to 2 inches of fine or double-shredded mulch, which packs down more. The Morton Arboretum suggests 3 to 4 inches for medium to coarse material.
Do I need to remove old mulch first?
Not usually. Measure the depth of the old layer and enter it as the existing depth. The calculator only adds enough to reach your target, which keeps the total within the recommended range.
How do I mulch around a tree?
Choose the ring shape. Enter the outer diameter of the mulched circle and the bare circle you will leave around the trunk. Keep mulch off the trunk: Penn State suggests pulling it back 3 to 5 inches from young trees and 8 to 10 inches from mature ones.
Is bulk mulch cheaper than bags?
Often for larger jobs, but delivery fees can flip the result for small ones. Enter the price per bag, the price per cubic yard and the delivery fee, and the calculator shows which is cheaper for your area.