About this mulch calculator
Mulch volume = length × width × depth in inches ÷ 12, in cubic feet; divide by 27 for yards. A 20 × 4 ft bed at 3 inches is 20 cu ft, or 0.74 yd³: ten 2 cu ft bags or seven 3 cu ft bags. One cubic yard covers about 108 sq ft at 3 inches.