Mulch Calculator
Mulch for a bed, as volume and as bags.
Bags or bulk
A cubic yard is 13.5 of the common 2 cu ft bags. Above about a yard and a half, bulk delivery usually wins on price; below that, bags win on convenience and a dry car. This bed (12 x 4 ft at 3 in) needs 0.44 yards, which is 6 bags.
Depth matters more than coverage charts say
Under 2 inches, mulch fails at its main job of suppressing weeds and holding moisture. Over 4 inches, it suffocates roots and invites voles. Keep it 2 to 3 inches in beds, and pull it back a few inches from trunks and stems; the 'mulch volcano' around a tree is slow strangulation.