How much mulch do I need?
One cubic yard of mulch covers 108 sq ft at a 3 inch depth, 162 sq ft at 2 inches, and 81 sq ft at 4 inches. That single fact answers most mulch questions. The calculator handles odd shapes, converts to bags, and covers rubber mulch, which is sold by weight because it is so much denser than wood.
The right depth actually matters
Three inches is the sweet spot for wood mulch on beds: enough to suppress weeds and hold moisture, not enough to suffocate roots. One or two inches lets weeds through; five or more invites fungus, holds too much water against stems, and wastes money. Around trees, keep mulch 3 inches deep but pull it back 3 to 6 inches from the trunk. The mulch volcano piled against bark that you see everywhere causes rot and girdling roots; flat donut, never volcano.
Bags versus bulk mulch
Mulch bags are typically 2 cubic feet, so a cubic yard equals 13.5 bags. Bulk mulch by the yard usually costs the same as 5 to 7 bags, which means bulk wins on price whenever you need more than about half a yard, if you have somewhere to dump it. Bags win on clean storage, exotic colors and small top ups. The bag count in the results uses the 2 cubic foot standard; check your bag size since 1.5 and 3 cubic foot bags exist.
Rubber mulch is a different animal
Rubber mulch weighs about 44 lb per cubic foot against wood mulch at 30, does not decompose, and is sold by weight in bags of 40 lb or by the pallet. Playgrounds use a 6 inch depth for fall protection, which is the preset above. It never needs topping up, but it also never feeds the soil, so keep it to play areas and paths rather than planting beds.