Mulch Calculator

How much mulch you need

Mulch is sold by the cubic yard in bulk and by the cubic foot in bags, and the only calculation is volume: length times width times depth. A 20 by 4 foot bed at 3 inches deep is 20 cubic feet, or 0.74 cubic yards — about 10 two-cubic-foot bags. Depth matters more than most people think: 2 inches suppresses weeds poorly and dries out fast, 3 inches is the standard recommendation, and more than 4 inches can suffocate roots and hold too much moisture against stems. Measure the bed, not the plants in it.

Bulk or bagged?

Bulk mulch is almost always cheaper per cubic yard, often by half, but it comes with a delivery fee and a pile on your driveway. Bags cost more per yard and create plastic waste, but you can carry them exactly where they are needed and store the extras. The crossover is usually around 2–3 cubic yards: below that, the delivery fee wipes out the bulk saving. This calculator shows both costs side by side so the comparison is explicit rather than a guess.

Applying it well

Pull old mulch back before adding new — layering fresh mulch on top of a compacted old layer just builds a mat that water cannot pass through. Keep mulch 2–3 inches away from stems and trunks: mulch piled against bark holds moisture and invites rot, the classic "mulch volcano" mistake. Water the bed before mulching, not after, so the soil underneath starts damp. And re-check the depth after a month: fresh mulch settles by about a quarter, so 3 inches applied becomes roughly 2.25 inches once it beds in.

Frequently asked questions

How deep should mulch be?

3 inches is the standard recommendation for most beds: deep enough to suppress weeds and hold moisture, shallow enough to let water and air reach the soil. 2 inches dries out fast; more than 4 inches can suffocate roots.

How many bags of mulch do I need?

Divide your volume in cubic feet by the bag size. A 20×4 ft bed at 3 inches deep is 20 cubic feet, or ten 2-cubic-foot bags. Enter your bed size above for an exact count.

Is bulk mulch cheaper than bags?

Usually yes — often by about half per cubic yard — but delivery fees apply, and you need somewhere to dump a pile. Below about 2–3 cubic yards, bags are often cheaper overall once delivery is counted.