Mulch formula
Cubic feet = area (sq ft) × depth (in) ÷ 12. Divide by 27 for cubic yards. One cubic yard covers about 108 sq ft at 3 inches, or 162 sq ft at 2 inches.
How deep should mulch be?
University extension services generally recommend 2–4 inches of organic mulch. Less than 2 in lets weeds through; more than 4 in can starve roots of oxygen. Keep mulch a few inches away from tree trunks—avoid “mulch volcanoes.”
Bags or bulk?
Bagged mulch is usually sold in 2 cu ft bags (13.5 bags = 1 cu yd). Above roughly 2–3 cubic yards, bulk delivery from a landscape yard is usually cheaper per yard.
Measuring irregular beds
Split the bed into rectangles (L × W), triangles (½ × base × height) and circles (3.14 × radius²) and add the areas.