How to use this calculator
Measure the planted area rather than the entire yard. For an irregular bed, split it into rectangles and calculate each one separately. Check the volume printed on your mulch bag; bag sizes vary.
The formula
A worked example
A 12 × 8 ft bed at 3 inches deep needs 24 cubic feet. With 10% extra, that is 26.4 cubic feet, or 0.98 cubic yards. Buy 14 bags if each contains 2 cubic feet.
Assumptions & limitations
Assumes a rectangular bed and an even depth. Extra allowance covers uneven ground or settling; it is not a recommendation for mulch thickness.
Common questions
How many bags make a cubic yard?
One cubic yard is 27 cubic feet. That is 13.5 bags at 2 cubic feet per bag; buy 14 whole bags to cover one cubic yard.
Does this account for mulch settling?
Only through the extra allowance you enter. Actual settling depends on the material and conditions.
Units reference
The calculation follows the method above. This reference supports the units and conversions.
NIST: SI units and conversion factors ↗Formula and worked example checked against automated test cases. About our methodology.